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Since the seismic performance of the bypass switch (BPS) cannot satisfy the stress safety factor requirement, an isolated combination of wire ropes with linear viscous dampers was employed. The assembled base isolation was designed using modal parameters, and the effectiveness of the isolation was validated numerically using finite element (FE) analysis and experimentally by the shaking table test. The numerical study shows that wire rope isolation can reduce the stress of a BPS considerably. Furthermore, the implementation of supplementary viscous dampers can further reduce the stress and, more importantly, displacement response, which is significant for UHV equipment. The middle section of BPS generates obvious high frequency vibration during test, although the root section still experiences the maximum stress response. Besides, testing verified the reliability of the FE model and confirmed that the stress safety factor requirement was satisfied. Therefore, the isolation comprised of wire ropes and a viscous damper is proposed to improve the seismic performance of the slender 800 kV composite BPS.

The final publication is available at Elsevier via https://doi.org/10.1016/j.engstruct.2019.05.064. © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

The conventional reinforced concrete Moment Resisting Frames (MRFs) have suffered from soft story failure during major earthquake events. A novel system of steel Energy-Dissipative Rocking Column (EDRC) is proposed to mitigate seismic responses of MRFs. Pseudo-dynamic tests are conducted on large-scale two-story and two-bay reinforced concrete frames, with and without EDRC, respectively. The post-earthquake behavior of these two systems is also compared through quasi-static cyclic tests. The experimental results show that the presence of EDRC can effectively mitigate the maximum value, residual value and inhomogeneous distribution of inter-story drifts, and thus prevent the soft story failure of MRFs. It is found that the maximum and residual inter-story drift of combined MRF and EDRC systems is reduced by 26.0% and 82.0%, respectively, compared to pure MRFs. The inhomogeneous degree of inter-story drifts can be reduced by 25.0% and 11.0%, respectively, in the pseudo-dynamic and quasi-static tests.

Post-installed reinforcement (PIR) bars helps to facilitate retrofitting works, mitigate misplaced reinforcement problems, as well as support newly casted additions. However, the use of PIR has not been addressed in the major reinforced concrete (RC) design codes worldwide. Recently, the European standards have introduced a beneficial coefficient of moments in EN 1992-4 2018 for concrete fastenings which allows compliant PIR systems to be designed by using the bonded anchor (BA) design method. However, when applying this method to wall-slab connection design, the moment resisting capacity is often limited by the lack of bar spacing and small concrete covers. This means that the method neglects long embedment depths and the connections designed based on this method are prone to brittle failure. In this paper, the strut and tie model (STM), which can better describe PIR with long embedment depths, together with the fundamental reinforced concrete (RC) theory is used to improve the ductility of moment connections with PIR bars. An experimental study is conducted to explore the structural behaviour of applying PIR bars that connect the wall and slab. Validations on the proposed STM and supplement to the BA design methods are made. From the experimental findings, measures are then proposed to enhance the ductility of the moment connections.

The development of the concrete industry has facilitated the use of nonconventional concrete types, such as high-strength concrete (HSC) and self-compacting concrete (SCC). Normal concrete (NC) beams experience a significant reduction in their strength after fire exposure. An experimental program is designed to investigate the effect of different levels of temperature on the most common concrete types and the effect of different retrofitting techniques to restore the capacity of reinforced concrete beams. Thirty-one beams were casted using NC, SCC, and HSC. Twenty-eight beams were subjected to temperatures of 400 °C and 600 °C for 60 min and 120 min to evaluate the beam behaviour under indirect fire conditions. Carbon fibre reinforced polymer (CFRP) laminates, bonded steel plates, and concrete jacketing have been used for beam capacity retrofitting. The exposure time at a high temperature level had a significant effect on the behaviour of the different beams, especially those with NC, which underwent a dramatic reduction in strength after being subjected to 600 °C for 2 h. The SCC beams had an acceptable behaviour under elevated temperature conditions. All the retrofitting techniques had a positive effect on SCC and HSC beams, but the bonded steel plate and CFRP techniques did not produce a noticeable effect on NC at 600 °C. The reinforced concrete jacket had a satisfactory effect in the drastically deteriorated beams.

The paper discusses the numerical analysis of all-steel buckling-restrained braces. These devices are designed to work in an inherently unstable regime, and their behavior is acutely sensitive both to any configuration detail in reality, and to any adopted parameter in their analysis. Their dissipative axial behavior can be reasonably well predicted by any suitable FEM model, if a good constitutive law is available. Nevertheless, it is shown here that an apparently accurate FEM calculation of the lateral contact forces, generated by the buckled core when it contacts the external containment profiles, produces results so sensitive to modelling details that they are practically devoid of an acceptable degree of accuracy. These observations might raise some doubts about the advisability of employing this type of bracing in normal engineering practice. In our viewpoint, a similar conclusion could be reached for any structural element designed to work in an unstable regime, unless the imperfections – of any type, including possible modelling details – could be explicitly taken into account, either parametrically or in a statistical way.

Evidence theory can be used for propagation analysis of structural response with various uncertainties because of its much more flexible and universal framework. However, the discrete characteristic and the ambiguity measure of the propagated result have severely influenced the practicability of evidence theory. Because of the basic probability assignment (BPA), the evidence domain is a countable region composed of all focal elements. Hence, in this study, an efficient uncertainty propagation method is proposed through evidence domain analysis. A multiple linear segment approximation for limit state equation (LSE) rather than structural performance function is firstly constructed, so the support degree of each focal element is directly judged in evidence domain. Then, the belief (Bel) measurement and plausibility (Pl) measurement are calculated by the positional relation of each focal element in the uncertain variable domain without involving response domain. Meanwhile, a volume ratio that can represent the proportion of focal element partly supporting event is calculated by utilizing the approximate LSE. Therefore, a maximum entropy probability measurement between the Bel and Pl can be provided using the volume ratio. One numerical example and two engineering applications are investigated to demonstrate the effectiveness of the proposed method.

Engineered cementitious composite (ECC) is a typical fiber reinforced cementitious composite with a strain-hardening behavior in tension and can be easily applied to strength masonry structures. This work studies the static behavior of flexural-failure dominant unreinforced masonry (URM) walls strengthened with ECC overlay. Five URM walls were constructed and four of them were reinforced: a wall strengthened with steel mesh, a wall strengthened with single-side ECC overlay, two walls strengthened with double-sides ECC overlay. One of the two double-sides ECC-strengthened walls was designed with a tie column. The effectiveness of reinforcement plans and tie column on the failure mode, lateral strength, hysteresis response, stiffness degradation, energy dissipation capacity, residual displacement and equivalent viscous damping is analyzed. The experimental results indicate that the ECC retrofit techniques can significantly improve the ductility of URM walls. The walls strengthened with ECC overlay exhibit significant increase in the wall drift and energy dissipation and decrease in the residual displacement. Finally, a calculated model for the ECC reinforced walls was proposed to estimate the maximum lateral strength.

In this paper we derive closed-form expressions for the autocorrelation functions of the response for uniform beam placed on elastic foundation and subjected to axial deterministic load. The excitation is represented as the white noise in time, and ‘rain-on-the-roof’ excitation in space. The boundary conditions of simple support are discussed. The normal mode approach is utilized, with explicit summation of the infinite series.

This paper presents the results of an experimental programme to investigate the performance of a new composite shear connector that can be used to build deconstructable composite floors. A total of 21 push-out tests were conducted to quantify the effects of different design parameters, including different nominal temperature levels (20 °C, 100 °C, 300 °C, 450 °C, 600 °C), with the steel decking perpendicular and parallel to the steel section, two different embedded shear stud lengths and two different grades of concrete (C40/50 and C20/25). The tests were mainly carried out under steady-state condition where the specimen temperatures were increased to the desired target and the load was then applied until failure of the specimen. A few transient tests were also carried out, in which a load equal to the load carrying capacity of the steady-state test at 600 °C was applied, followed by increasing the specimen temperature until failure. Three modes were observed: (i) concrete crushing with stud fracture, (ii) stud fracture and (iii) concrete pull-out. Concrete pull-out occurred only on one specimen with concrete grade C20/25. It is found that the main failure mode at elevated temperatures not exceeding 400 °C was initiated by concrete crushing, concomitantly producing ductile stud damages. At elevated temperatures above 400 °C, the failure mode changed to shear stud fracture. The Eurocode 4 calculation equations were shown to produce shear connector resistances to be in reasonable agreement with the steady state results for the higher-grade concrete, even though the previous equations were developed for welded shear studs. The transient state tests failed at lower temperatures than the target temperature of 600 °C, indicating it may not be safe to use steady state tests for evaluation of shear connector resistance at high temperatures.

Concrete-filled steel tubes (CFST) are increasingly used thanks to the improved structural performance, especially under compression. This is basically due to the confinement effect provided by the tube, which usually enhances ductility and strength of concrete infill. Several researchers have been focused these last decades on these sections under different assumptions, especially those issues which derive from the construction process; the fact of loading the tube before concreting in preliminary constructive stages leads to a preloading stress which implies a different response of the section than the expected. These issues must be considered in the design process and derive into undesired preloading effects on one of the two components derived from the process itself. Nevertheless, few studies treat the fact of preloading as a design method itself before being under service loads (active methods) to enhance the capacities of CFST sections. This paper analyses and compares 4 different methodologies (2 passive versus to 2 active preloading methods) by describing the potential benefits and consequences of them on the whole section; while sometimes a pre-stress ratio on one component may enhance the global mechanical response, sometimes it does not and becomes even harmful. The ratio of confinement effect over the core and especially when it becomes activated reveals the grade of real enhancement of the compressive response of the section in terms of ductility and strength.

The outrigger system is an effective solution in mitigating seismic responses of core-tube-type tall buildings by mobilizing the axial stiffness of the perimeter columns. The concept of damped-outrigger has been proposed which introduces dampers in the outrigger system to dissipate seismic energy. This study investigates the seismic behavior of a damped-outrigger system incorporating buckling-restrained brace (BRB-outrigger). The outrigger effect combined with the energy dissipation mechanism of the buckling-restrained brace (BRB) effectively reduce the seismic response of the building. This study proposes the methods to evaluate the inelastic seismic response of structures with multiple damped-outriggers based on a spectral analysis (SA) procedure. For the structure with BRB-outriggers, the optimal outrigger elevations, and the relationships between the axial stiffness of the BRB, the axial stiffness of the perimeter column, and the flexural rigidity of the core structure in order to minimize the seismic response are the primary research objectives of this study. Analytical models with building heights of 64 m, 128 m, 256 m, and 384 m are used to perform the SA and the nonlinear response history analysis. This study concludes with a design recommendation for preliminary design purposes.

Experimental research is conducted to investigate the flexural behavior of corroded High Performance Steel (HPS) beams. Four beams with various corrosion damage are designed and subjected to electrochemical accelerated corrosion process. 3D scanning technology is employed to analyze the geometric features affected by the corrosion damage. Flexural tests are carried out, and the impact of corrosion on the flexural response is discussed. Considering the randomness of corrosion pits in each area, predictive models are proposed for the flexural strength of corroded beams with an idealized elastic-plastic and linear-hardening constitutive relationship model. An analysis comparing the proposed models with Chinese and American codes is made. Results show that increasing the corrosion damage leads to a decrease of discreteness in the residual sectional area and causes a transformation in the compressed flange from noncompact to slender. A corrosion loss less than 10% leads to slight deterioration of both strength and stiffness degradation, while further corrosion damage results in a significant decrease. The depth and length of the buckling wavelength for corroded beams decreases gradually as the corrosion damage become more serious. The analytical models IEM and LHM or the GB50017-2017 may be suitable for predicting the lower and upper limit values of the ultimate flexural moment, respectively, and results predicted by AISC are conservative.

This paper presents an analytical model developed to predict the flexural load-deformation behavior of reinforced concrete members containing tension lap splices. The proposed model incorporates the effect of reinforcement slip of the lap splice and the effect of high strain rates on bond characteristics and material properties of concrete and steel. The main advantages of the proposed model are that bond-slip phenomena are captured through the use of pseudo-material stress-strain relationships, rather than giving consideration to the continuum of reinforcement and slippage over the entire structural element. Material properties and associated dynamic increase factors (DIF) are defined using accepted formulations. A suitable bond-slip law is presented and modified to account for the influence of strain rates on bond characteristics. Beam failure criteria are expressed in terms of a flexural failure of the member or a bond splitting failure of the splice. A comparison of the analytical predictions with experimental data demonstrated that the proposed analysis technique can reasonably predict the flexural response of beams with tension lap splices. The results also show that the model is equally applicable for use at low- and high- strain rate loading, such as those generated during blast and impact loading.

Base pipe pin connections were developed to simulate a hinge behavior at the base of cast-in-place or precast bridge columns. Base pipe pins are composed of two steel pipes: one pipe is embedded in the column and the other in the adjoining member. Shear force is transferred through contact of the pipes and friction. The uplift force is resisted by a tension member and welded studs on the surface of the column pipe. To investigate the behavior and failure mode of base pipe pins under direct tension and to determine the ultimate tensile capacity of the pins, two scaled pipe pin connections were tested under direct tension. Elaborate nonlinear finite element (FE) studies of the pipe pins were also conducted to explore the effects of different parameters on the response of the pins. There are many possible failure modes that could occur under tension. Test results depicted that rupture of the pin tension member with no damage to the connection was the dominant failure mode in pure tension. The FE models accurately estimated the response of the test models and the observed failure mode. The analytical results showed that decreasing the pipe height alters the failure mode but does not affect the ultimate capacity of the connection significantly. Furthermore, reducing the pipe height or increasing the number of stud layers has a small effect on the ultimate capacity and stiffness of the connections.

The article deals with the analysis of the probability of failure of a load-bearing steel bridge member under bending. The focus is on fatigue failure caused by stress cycles from multiple repeated traffic loading on the bridge. Failure is defined by the occurrence of a fatigue crack of critical size. Crack propagation and the fatigue limit state are described using linear fracture mechanics. The failure probability is a function of the equivalent stress range, initial crack length, Paris exponent, number of load cycles (stress changes) increasing over time and other input random variables. The failure probability is evaluated in time steps and then studied using a new type of global sensitivity analysis subordinated to contrasts. The results of the sensitivity analysis show that the first (second) dominant variable is the equivalent stress range (initial crack length) at any given point in time of the bridge operation. Strong main effect of equivalent stress range is associated with higher values of failure probability at the end of the lifetime of the bridge. Small values of failure probability are strongly influenced by interactions among input variables, which cannot be expressed as the sum of main effects of the individual input variables. The main and higher-order indices of each input variable are supplemented by displaying its total index. The direct goal of probability and sensitivity analysis is structural reliability. Sensitivity analysis confirms and deepens the knowledge gained from the time-dependent probability analysis. The numerical example illustrates the rationality of probability-oriented sensitivity indices and the feasibility of their estimation using Latin Hypercube Sampling (LHS). In addition, structural reliability is studied using Bayesian probability, which identifies the times for planning bridge inspections.

Prediction of peak wave heights early in the TLD design process is critical to ensure proper tank freeboard is allocated. If insufficient freeboard is allocated, the performance of the TLD may be adversely affected by the waves impacting with the tank ceiling. A frequency domain model is developed to predict the spectral response of the first two TLD sloshing modes. A probability density function of the wave height envelop for the first two sloshing modes is derived and employed to predict the peak wave height expected during a specified duration of time. Scale-model structure-TLD tests and nonlinear simulations are employed to evaluate the proposed frequency domain model. The model predicts the RMS response of the second order sloshing mode within a relative error of 15% when compared to simulations. The error increases when the water depth ratio is small. The predicted peak structural responses are in excellent agreement with those that are simulated or measured. The predicted peak TLD wave heights show a maximum error of 20% for all the cases considered. The peak factor relating the peak wave height to the RMS response of the fundamental sloshing mode increases with a decreasing liquid depth and increasing RMS response amplitude. The proposed model enables a rapid estimation of the peak wave response without resorting to computationally expensive nonlinear time domain simulations.

Parameter identification of cables in the operation period is a significant issue related to the state of serviceability and safety evaluation of cables. A generalized characteristic function is established based on the dynamic stiffness theory to identify cable parameters in the study. The characteristic function exhibits an analytical form. The function relatively fits actual engineering cables due to comprehensively considering cable bending stiffness, sag, inclination, etc., and thus it is a relatively accurate inverse-analysis model of cable parameters. The variation of bending stiffness and cable force with different geometric parameters and the influence of geometric parameters on the identification accuracy of the two parameters are investigated based on numerical analysis. And a parameter identification method based on the H-I ridges of inverse-analysis characteristic function is proposed. The proposed method identifies cable parameters using the multi-order frequencies of cables simultaneously, and the order of modal frequencies and the fundamental or lower-order frequency are not required in the application of the proposed method. Finally, the results of tension tests on two real cables with lengths of 20 m and 168 m verify the applicability of the inverse-analysis characteristic function and the parameter identification method proposed in the study.

The bond behavior of reinforcing bars embedded in concrete has been widely evidenced to exhibit an obvious nonlinearity with a high degree of randomness. To cope with this phenomenon, a stochastic damage model based on an innovative spring system is proposed in this paper. To describe the stochastic feature of bond response, the model introduces a random variable that specifies the failure displacement of micro spring elements, and meanwhile, two evolution laws for the interfacial damage and sliding are also defined respectively. Moreover, the effects of loading history and lateral stress are incorporated into the model, which is capable of reproducing the path-dependence and pressure-sensitivity of bond behavior faithfully. Finally, the model is numerically implemented by exploiting an implicit backward Euler scheme and verified by a number of numerical trial tests and independent experimental results. The satisfactory validations may provide a beneficial reference to bring the stochastic nature of nonlinear interfacial debonding into future theoretical studies on the structural response of reinforced concrete structures.

This paper presents the results of the numerical analysis of concrete dam structures which are affected by Alkali Silica Reaction (ASR) and subjected to seismic load. In this research a Chemo-Thermo-Mechanical ASR Finite Element numerical code is developed to model and analyse this phenomenon in concrete dams. It considers the effects of variables such as temperature, non-uniform time-dependent material degradation and 3D stress confinement on ASR evolution. The model is validated by modelling the mechanical response of the Fontana gravity dam and comparing the results with the actual data on macro crack appearance and crest displacement. While the structural behaviour of ASR affected structures under monotonic and quasi-static loading has been extensively investigated over the last decades, limited research has addressed the effect of dynamic loads on structures affected by ASR. The combined effect of old and new cracks under dynamic excitation may cause dam failure. The numerical simulations are used to assess and predict the dynamic stability of the Koyna dam considering fluid-structure interaction and are also used to investigate the evolution of damage associated with inception and development of macro cracks in the dam structure due to the combined effect of the synthetic ASR and realistic seismic loading on the dam. The results show that this combined action can significantly change the dynamic behaviour of typical concrete dams due to concrete material degradation and crack development.

This study investigated the crack width movements of a continuously reinforced concrete track (CRCT) of railways subjected to environmental loads, such as changes in temperature. To this end, in-situ experiments were carried out at two railway CRCT sections. There are two different types of cracks in CRCT namely the contraction (top-down) crack and reflection (bottom-up) crack. The behaviors of the contraction and reflection cracks were thoroughly analyzed and the differences in the crack width movements were investigated. The relationship between crack width movements and transverse locations was also evaluated. Based on the findings from this comprehensive experimental study of crack widths, we proposed multiple methods to improve the performance of CRCT.

This study investigates the seismic performance of a newly developed self-centering bracing system using a novel experimental technique named as closed-loop dynamic (CLD) testing. The bracing, named piston-based self-centering (PBSC) apparatus, employs Ni-Ti superelastic shape memory alloy (SMA) bars inside a sleeve-piston assembly for its self-centering mechanism. During cyclic tension-compression loading, the SMA bars are only subjected to tension avoiding buckling and leading to flag-shaped symmetric force-deformation hysteresis. Initially, a braced frame building fitted with PBSC is seismically designed and the preliminary sizing of the brace is determined. For testing, considering the lab capability, the brace is fabricated at a reduced scale. The process of “Closed-loop dynamic testing” starts with the brace test (step 1) under strain-rate loading to characterize the numerical model parameters (step 2), which are then scaled-up as per similitude law and implemented in a finite element software, S-FRAME’s PBSC brace model (step 3). Then the braced frame building is analyzed under an earthquake (step 4) and the axial force-deformation response of the brace under consideration is captured (step 5). In order to further understand and validate the actual response of the brace under earthquake type loading, the axial deformation obtained from S-FRAME is scaled-down (step 6) and used as input parameters for testing the reduced scale brace (step 7). The obtained response (step 8) is further scaled-up and used to match the S-FRAME’s PBSC model for validation (step 9). Iterations from step 3 to step 9 will be required until the experimental and numerical results converge. Convergence criteria used for this validation include both the energy dissipation capacity and initial stiffness within 10% accuracy. Reasonable agreement between the numerical and experimental results is achieved in the closed-loop dynamic testing. The PBSC brace shows excellent self-centering capability under various earthquake loadings.

Traditionally, structural optimization is a numerical process; candidate designs are created and evaluated through numerical simulation (e.g., finite element analysis). However, when dealing with complex structures that are difficult to model numerically, large errors could exist between the numerical model and the physical structure. In this case, the optimization is less meaningful because the optimal results are associated with the numerical model instead of the physical structure. Experiments can be included in the optimization algorithm to represent complex structures or components. However, the time and cost limitations are prohibitive when iteratively constructing and evaluating complete structural systems. Real-time hybrid simulation (RTHS) is an efficient and cost-effective experimental tool that combines numerical simulation with experimental testing to capture the total structural performance. This paper proposes a framework for real-time hybrid optimization (RTHO); RTHS is used to evaluate the performance of candidate designs within the optimization process. The framework creates a cyber-physical optimization environment using RTHS, a modern experimental technique with roots in earthquake engineering. This paper outlines the framework for RTHO with accompanying proof-of-concept studies. In a preliminary study, the base isolation design of a two-story building was optimized for seismic protection. RTHO was further validated for the optimal selection of multiple semi-active control law parameters for an MR damper installed in the isolation layer of a five-story base-isolated building. Both cases used RTHS to evaluate the candidate designs and particle swarm optimization (PSO) to drive the optimization. RTHO is well-suited to evaluate nonlinear experimental substructures, in particular those that do not undergo permanent damage such as structural control devices. Structural damage, if of interest, can be modeled through the numerical component. This paper proposes and demonstrates the integration of state-of-the-art optimization algorithms with state-of-the-art experimental methods – a cyber-physical approach to structural optimization.

Vulnerability of adobe constructions under lateral loading has promoted efforts to explore a wide variety of techniques for their retrofitting. Following this trend, the present experimental study was designed and implemented to investigate in-plane lateral strengthening/repairing of adobe walls using near-surface-mounted (NSM) steel rebars. The experimental parameters were comprised of reinforcement ratio, axial pre-compression load, and initial damage. For this purpose, seven wall panels, including two control, two repaired, and three strengthened panels, were made of identical adobe units and mud mortar. All walls have a thickness of 200 mm, a length of 1020 mm, and an effective height of 700 mm. Testing was performed under an incremental lateral displacement reversals combined with a constant pre-compression axial load. The experiment was designed such that the as-built specimens would undergo their failure mode in the form of diagonal shear cracking. This provision was allowed the proper assessment of the adopted NSM retrofitting technique in terms of its efficiency to preventing this undesirable failure mode. Finally, the results were compared based on the hysteretic load-displacement curves and other structural parameters. The adopted technique was found to be effective not only in strengthening existing adobe walls, but also in rehabilitating significantly damaged ones.

The estimation of seismic demand that connects the ground motion intensity measure and the damage measure of structures is one of the most important components in the performance-based design. The random nature of earthquake ground motion with great uncertainties in structural properties has posed challenges before this estimation. In this study, the suitability of different scalar and vector intensity measures of ground motion is quantified by using information theory and relative entropy concepts in the representation of ground motion uncertainty. The multilinear demand models for a better estimation of the seismic demand of structures are developed for near-fault pulse-like and ordinary ground motions, separately. The results indicate that the measures based on the spectral acceleration, velocity, and vector values are more appropriate intensity measures in the low, moderate, and high levels of damage for pulse-like records, respectively. For ordinary records, the use of vector IMs is not recommended due to their complexities and slight superiorities to scalar IMs. If the evaluations require a simple IM in a single-linear demand model for all the damage, the measures of VSI and SIH would be recommended.

One of the prevalent seismic damage modes of skewed bridges is that the shear keys and/or other transverse retainers at the acute corners suffer severer damages than those at the obtuse corners. In practice, the retainers are usually designed and detailed as structural fuses to protect the substructure and foundation in high seismic zones. However, in low seismic zone, such as seismic zone 1 in AASHTO, they are designed elastic. In this paper, a parameter study was conducted to: (1) investigate the distribution of forces among the shear keys in skewed bridges and (2) evaluate AASHTO’s provisions for the minimum connection force of shear keys in low seismic zone. Parameters of interest include skew angle and expansion gap size. An experimentally validated numerical model was employed to model the prototype bridges with exterior shear keys. Nonlinear response history analysis was performed. The results show that when the longitudinal gap is closed for small to moderate gaps, the forces in the keys at the acute corners can be much higher than those at the obtuse corners. This is most likely to occur since the keys should resist the transverse loading along with the impact and friction forces at the abutment-deck interface caused by longitudinal motion. These higher forces of the keys at the acute corners could exceed AASHTO’s limit in low seismic zone. To reduce the forces in the keys, it is recommended that the gap be increased in size to avoid abutment pounding, which is an affordable solution in low seismic zone since the increase is expected to be small. Further, a Simplified Method is developed to estimate the maximum connection forces of skew bridges in low seismic zone. Good agreement was obtained between the Simplified Method and the FEM model. Therefore, the Simplified Method may be used for the preliminary design of shear keys.

When evaluating the probabilistic seismic performance of a structure in the context of Performance-Based Earthquake Engineering (PBEE) applications, only estimates of the true response are obtained due to the finite size of the group of records selected to represent the seismic scenario. The proposed study examines the variability of these estimates, in terms of fragility parameters and failure rates, by implementing a procedure that creates seismic scenario-consistent groups of records based on regrouping criteria applied to a larger set of records. The results are then compared to those obtained from a statistical approach based on the bootstrap resampling procedure, whose validity is disputed due to its incompatibility with common applications involving probabilistic seismic performance assessment. Given that bootstrap resampling assumes that each bootstrap sample is random, this condition is incompatible with requirements involving the need to match specific spectral statistics of the group of records with a target spectrum. Due to the increased computational cost of the procedure based on regrouping criteria, the effect of this incompatibility is analysed by examining the agreement between the two procedures for several case studies and the conditions under which bootstrap resampling leads to a reduced level of error. Further insights about the variability of the estimates are obtained by analysing scenarios with deterministic and probabilistic thresholds of the limit state capacity. Among other aspects, the results show that, for both capacity thresholds, bootstrap resampling can provide acceptable results as long as a sufficient number of ground motions and number of stripes are used.

During testing of the structural reliability of a prestressed reinforced concrete bridge built in the late 1960s, the author compared the structural responses, performances and costs of jointly conducted static and dynamic load tests. In the static load test, the precision spirit leveling technique was used to measure the deflections of the deck induced by four trucks weighing about 36 tonnes each. In the dynamic load test, accelerometers placed on the main beam were used to measure the vibration frequencies following an impulse produced by a 2-tonne truck. The dynamic load test resulted in a refined finite element model of the bridge. The comparison showed that the dynamic load test can supplement the static load test for the structural testing of new bridges or be an alternative to it for the monitoring of operational bridges.

This paper presents a new strengthening method for existing frames by using outside sub-structures, namely, precast bolt-connected steel-plate reinforced concrete (PBSPC) frame-braces. The working principles, numerical methods, and design procedures are presented, and case studies are carried out. The simulation results were consistent with the results from previous experiments, indicating the effectiveness of the numerical model. The design objective and procedure were put forward, and during the process, a coefficient η that considers the precast influences was considered. A practical engineering retrofitting was performed based on the proposed numerical model and design process, where the structure was subjected to the design basis earthquake (DBE) and maximum considered earthquake (MCE). The analyses demonstrated that the structural demands were clearly reduced within the thresholds, and the inner force was transferred from the existing building to the external sub-structure after strengthening. The incremental dynamic analysis (IDA) and fragility curves were plotted, illustrating the greater reliability in structural capacity and the lesser possibility of structural damage with the new upgrading form.

This work is motivated to determinate the optimal design for various types of Dynamic Vibration Absorbers (DVAs) under the effect of random loads. These devices are the following: DVAs connected in parallel or series; two degree-of-freedom traditional dynamic vibration absorber (2dof-TVA) with translational and rotational motion; and inerter-based DVAs (IDVA-C6, C4, and C3). These types of DVAs were selected by their high effectiveness for suppressing vibration however a comparative study on their dynamic performance has not yet been performed. Two different excitation sources of random loads are studied in this paper which are random ground motion and force excitation. An optimum design for majority of these devices has not yet been computed when subjected to random ground motion excitation, and therefore in this paper are computed. For random force excitation, some numerical solutions for the optimal design of these devices have not yet reported which in this paper are computed in order to compare the dynamic performance for each device with respect to that of the classic DVA. For both random excitation cases, the H 2 optimization criteria is used to analytically compute the variance of squared modulus of frequency response of the undamped primary structure, and then nonlinear unconstrained optimization problems are formulated in order to obtain the optimal design. Numerical solutions revealed that the IDVA-C6, C3, and DVAs connected in series presents more than 13% and 10% improvement with respect to the classic DVA for random ground motion and force excitation cases, respectively. These devices can widen the suppression band (SB) from 30% to 40% for mass ratios values from 1% to 10%. It means that devices are more effective and robust for mitigating vibration than the classic DVA. In addition, the rotational inertial double tuned mass damper (IDVA-C6) has the same relative dynamic performance (RDP) and suppression band index (SB) than the double-mass dynamic vibration absorber arranged in series. For practical application where the mounting space of the DVA is extremely reduced, the DVAs connected in series could be more convenient to use than IDVA-C6. The concept of equivalent mass ratio is introduced in order to explain the superiority of these devices with respect to the classic DVA. Finally, in H ∞ optimization criteria, the IDVA-C6 presents the same vibration amplitudes at all excitation frequency range and suppression band than DVAs connected in series.

Beam-column assemblies of many existing reinforced concrete (RC) buildings are typically designed and built before the development of the current seismic codes; that may permanently fail in non-ductile behaviors, including column flexural hinging or joint shear failure mode, during ground motions. The current experimental research, therefore, was conducted to evaluate the efficiency of newly proposed rehabilitation schemes in retrofitting of deficient RC beam-column connections using fiber reinforced polymers (FRPs). To do so, five half-scale exterior beam-column joints were constructed and tested under constant axial and reversal-cyclic lateral loadings. The joint specimens were designed with strong beam-weak column theory and insufficient transverse reinforcement in the joint region. Of these, four specimens were strengthened with CFRP sheets and the remaining specimen was used as a control. In the strengthening patterns, to eliminate any surface debonding of FRP, the recently developed externally bonded reinforcement on grooves (EBROG) method was used. Besides, CFRP anchor fans were employed in the beam-column interface to completely anchor the longitudinal FRP sheets and also transfer the forces between the beam and the column. The test results showed that the adopted strengthening schemes successfully prevented the brittle failure of the specimens and were able to provide a more ductile mechanism by relocating the plastic hinge away from the weak column and the joint zone toward the beam. Furthermore, a significant enhancement was observed for specimens in terms of their strength, ductility and energy dissipation up to 73%, 139%, 144%, respectively. Additionally, the EBROG technique together with the CFRP fans at the interface of the beam-column joints eliminated any debonding or slipping of the longitudinal CFRPs.

This paper aims to clarify flexural cracking behaviors (e.g., crack width and crack spacing) of a lightweight deck system composed of steel orthotropic deck and thin ultra-high performance concrete (UHPC) layer. Forty steel-UHPC composite plates and eight steel-UHPC composite beams were tested to explore their cracking characteristics in transverse and longitudinal directions, respectively. The influences of reinforcement ratios, the thickness of the UHPC cover, the spacing of stud shear connectors, and the depth of the UHPC layers on cracking behaviors were examined. According to the bridges with composite deck systems recently constructed in China, the same spacing of reinforcing bars were employed in longitudinal and transverse directions, which ranged from 30 and 75 mm. The test results show that the occurrence and growth of cracks in UHPC layers could be effectively restricted by increasing reinforcement ratios, reducing the thickness of UHPC cover and the spacing of stud shear connectors, as well as thickening the UHPC layer. For the average crack spacing, the most significant factor was the reinforcement ratio. For the longitudinal behavior of the lightweight deck system, the steel-UHPC composite beams would fail due to the yield of steel U-ribs and the crack width in the UHPC layer would be small (e.g., 0.09–0.14 mm) when the reinforcement ratio and the thickness of UHPC cover are design appropriately. Based on the experimental observations, the formulas were developed to estimate the stress in reinforcements for the composite (steel + UHPC) lightweight deck system. The reinforcement stresses predicted by these formulas were in agreement with the experimental data. A new formulation for predicting the maximum crack width in composite (steel + UHPC) lightweight deck system was also proposed. Good agreements were achieved between the test results and the predicted values of the flexural crack width.

In this study, a series of new beam-column connections was proposed for large-span steel hyperbolic towers. The mechanical performance of the connections under an out-of-plane bending moment and a shear force was studied via experimental tests and numerical simulation. Different parameters such as the connector type, row number of the bolts, and plate thickness were considered during the study. The moment–rotation curves and main failure modes of the connections were obtained and discussed in detail. The results showed that the new beam-column connections proposed in this paper had excellent bending stiffness and ultimate bending capacities. In addition, the finite element model of the connections was established by ABAQUS software, and the experimental and numerical results were compared. The comparison results showed that the numerical model could predict the moment–rotation curve and different failure modes accurately. The new joint system and study presented in this paper are relevant references for the study of large-span steel hyperbolic towers, which are increasingly becoming the prominent options compared with concrete cooling towers.

Compared to unstiffened circular hollow section (CHS) X-joints, CHS X-joints stiffened with external ring stiffeners and gusset plates have exhibited much higher bearing capacity. To gain insight into the effects of the chord pre-loads on ultimate bearing capacity, this paper presents results of finite element (FE) analyses of the stiffened X-joints with braces under compression and chord under (i) axial load, (ii) in-plane bending moment, or (iii) combinations of axial load and in-plane bending moment. Precision of the FE model under combined brace and chord loads is validated by test results. The ultimate bearing capacities attained by using proportional loading and non-proportional loading respectively are presented, and the results indicate that the differences due to loading path are negligible. The validated FE modelling technologies are then employed in a parametric study on the effect of chord pre-load. A total of 4560 stiffened X-joints are examined in the parametric study. The theoretical analysis presented herein provides a reasonable explanation for the significant reduction in strength of stiffened X-joint when the chord is under axial tension. Finally, a chord stress function with corresponding boundary conditions is proposed, in which the coefficients for different chord load cases are determined through regression analysis. Furthermore, a lower-bound multiplier is given for the function to ensure a conservative design.

Detailed finite element (FE) models with 3-D solid elements are typically used to simulate impact behaviors of reinforced concrete (RC) beams and columns. However, the method usually requires a substantial amount of time and effort to model concrete and reinforcement and conduct nonlinear contact-impact analyses. Also, the accuracy of the method cannot be guaranteed due to the limitations in concrete material models implemented in general-purpose FE codes. In this paper, an efficient modeling method is proposed to capture both flexural and shear behaviors of RC beams and columns under low-velocity impact loading. A macroelement-based contact model was developed in the proposed method to capture interaction behaviors between impacting objects and RC members. In the contact model, a compression-only spring with an initial gap behavior was used to account for the stiffness and the kinematic response of an impacting object, and a combination of an elastic spring and a viscous damper in parallel was employed to simulate the contact stiffness and damping. By properly approximating the strain-rate effects, traditional fiber-section elements were demonstrated to be capable of predicting impact-induced flexural failures for RC members. On this basis, a general approach for both flexural- and shear-critical RC columns under impact loading was presented with the inclusion of additional shear springs in the fiber-section elements. Nearly fifty impact tests on RC beams and columns reported in the literature were employed to validate the proposed modeling method. Comparisons between the experimental and numerical results indicate that failure modes of the impacted members can be identified explicitly by the use of the proposed modeling method. Also, reasonable agreements were achieved for the impact forces and the impact-induced responses obtained from the impact tests and the analyses. The proposed method can be readily implemented without coding in any FE software as long as traditional fiber-section elements, and discrete macroelements are available. This feature would offer an advantage for the applications of the proposed method such as when assessing the structural response and vulnerability of a bridge structure subjected to vessel and vehicle collisions.

Reinforced concrete (RC) walls have been widely used in tall building construction to resist lateral loads. However, RC walls behave low ductility and limited deformation capacity under high axial force ratio. Due to the brittle behaviour of high-strength concrete, it was seldom used in RC walls though it has a vast of merits compared with normal-strength concrete. To further push up the limit of concrete strength, i.e., beyond 80 MPa in practical wall construction and to figure out a possible alternative of river sand due to the sustainability and environmental friendly requirement, an innovative wall, namely ring-stirrup concrete-filled-steel-tube (CFST) composite wall with high-strength manufactured sand concrete is proposed. The proposed composite wall consists of two CFST columns embedded at each boundary element and several stirrups in the form of continuous ring along the entire section. A series of quasi-static tests based on orthogonal experimental design method (Taguchi method) are conducted to investigate the seismic behaviour of the composite walls. The experimental parameters are axial force ratio, steel ratio in CFST columns and volume ring-stirrup ratio. From the experimental tests, it is concluded that the proposed confining schemes are highly effective in improving the seismic behaviour of the walls. Moreover, the effects of these three parameters on the peak strength, ductility and energy dissipation capacity of the walls have been investigated. Finally, a design approach considering the confinement effect of CFST columns is proposed and verified to evaluate the lateral load-carrying capacity of the proposed walls.

This paper evaluates the behaviour of reinforced concrete (RC) slabs strengthened in shear with prefabricated L-shaped carbon fibre–reinforced polymer (CFRP) laminates. Four large scale slabs were tested; one slab was kept without strengthening and the other three slabs were strengthened with L-CFRP laminates using different configurations. The behaviour of the slabs strengthened with L-CFRP laminates was compared with that of a similar slab without shear reinforcement. The details of the strengthening methods implemented in the study, experimental setup and parameters of all the material used are provided. The experimental results are presented including deflection, strain readings and rotation as well as the crack pattern of each specimen. The test results reveal that using post installed L-CFRP laminates can significantly improve the punching shear capacity and deformation capacity of RC slabs. Further, the strengthening technique can also be used to prevent sudden collapse of buildings after punching shear failure by increasing the post punching deformation of slabs. The experimental results were compared with the theoretical results predicted by ACI 318 (2011), Eurocode 2 (2004) and Fib Model Code (2010).

Large-span spatial structures are quite sensitive to wind load because of their notable structural flexibility and low fundamental frequency. Structural health monitoring (SHM) of wind applied to this type of structure is the most direct and effective method of guaranteeing their safety. However, SHM produces a large amount of observation data, and these data often contain compressible redundant information and are usually sparse in the amplitude-frequency domain. To improve their transmission efficiency and quality and explore the characteristics of measured wind load on the surface of a large-span roof, we proposed l p -norm ( 0 p 1 ) sparse regularization based on compressive sensing for compression and reconstruction of wind speed data in the amplitude-frequency domain. The present compressed data were obtained through a low-rate sparse sampling method according to compressive sensing theory, which is more robust than the traditional sampling method. The alternating direction method of multipliers and the l p shrinkage method were applied to solve nonconvex optimization of reconstructing original data from incomplete measurements. The effectiveness of the proposed method was verified through a field test on a large-span steel roof of a railway station in southern China. The experimental results showed that the proposed method was superior to the smoothed l 0 method and typical l 1 based on the fast iterative shrinkage thresholding method. The reconstruction error was very low; even when the sampling rate was 10%, the signal-to-noise ratio of the reconstruction signal was 21.27, and the absolute error of reconstruction was 0.05 . In addition, the distributions of wind power density and wind rose were consistent before and after compression.

This paper numerically investigates the dynamic response and power capture performance of a Very Large Floating Structure (VLFS) with a Wave Energy Conversion (WEC) unit. The VLFS is composed of two hinged modules of which the relative pitch motion induced by waves is converted into electricity by the WEC unit. The discrete-module-beam-bending based hydroelasticity method is used to establish the equations of motion for the VLFS. A theoretical model is derived for optimizing the power take-off damping of the WEC unit. Based on the numerical results, it is found that (i) placing hinge near the foreside of VLFS is a good option for both the reduction of hydroelastic response and the enhancement of power absorption; (ii) for medium and long waves a larger wave incidence angle corresponds to a larger vertical displacement, a smaller bending moment and a decreased power capture width ratio of the VLFS; and (iii) the decrease of structural bending stiffness brings an increase of vertical displacement and a reduction of bending moment while its effect on power absorption is insignificant except for a very large bending stiffness.

Deviations from nominal design values of mechanical characteristics of seismic isolators are inevitable due to uncertainties and/or errors in material properties, element dimensions, construction methods, quality control, and/or installation steps, etc. In addition, due to uncertainties existing in active fault mechanisms affecting the site and local soil conditions, earthquake ground motions show record-to-record variability. Moreover, environmental conditions and/or time-dependent factors such as aging, temperature, and travel, etc. may also cause additional deviations in nominal values of characteristics of seismic isolators and thus in structural responses over the service life of structures. Therefore, in order to capture the dynamic behavior of base-isolated buildings realistically and design reliable base-isolated buildings, influence of such uncertainty should be taken into account. In this study, seismic reliability of realistic fully three-dimensional benchmark multi-story buildings equipped with nonlinear isolation systems is investigated under historical near-fault earthquakes. In order to take into account the uncertainties in the isolation system characteristics, pre-yield stiffness, post-yield stiffness, and yield displacement parameters are assumed as random variables, while the record-to-record variability nature of the ground motions is considered by using large sets of historical near-fault ground motions with or without forward-directivity effects. Two different levels of nominal isolation periods are taken into account while three different levels of uncertainty are considered for the random isolator characteristics. The reliability of the buildings is investigated in terms of structural integrity, isolation system safety, and the safety of the vibration-sensitive contents of the buildings using the peak bearing displacements and the peak floor accelerations obtained from the nonlinear time history analyses conducted in the framework of the Monte Carlo simulations. The plots including the average reliabilities for the displacement and the acceleration limit values provide a comprehensive picture in terms of the reliability level of the structural systems and of the vibration sensitive contents.

Civil engineering structures such as high-rise buildings and long-span cable-supported bridges usually exhibit low-frequency characteristics and the resultant response signals may be non-asymptotic (the amplitude change rate is higher than its phase change rate) and even have closely-spaced frequency components. The identification of satisfactory instantaneous frequencies of such response signals is a challenge faced by standard synchrosqueezing wavelet transform. The paper aims to propose a combined method to address this challenge. The proposed method combines an extended analytical mode decomposition (AMD) method, a recursive Hilbert transform and a zoom synchrosqueezing wavelet transform (consisting of frequency-shift operation and partial zoom synchrosqueezing operation). In the method, a multi-component signal, which may consist of closely spaced frequency components, is firstly decomposed into several mono-component signals by the extended AMD, and the extracted mono-components are then demodulated into asymptotic signals by recursively using the Hilbert transform. After that, a frequency-shift operation is employed to improve time resolution and a partial zoom synchrosqueezing operation is then applied to improve the frequency resolution in the narrow low frequency range of interest. Two numerical examples, an experiment on an aluminum cantilever beam with abrupt mass reduction and an experiment on a cable with time-varying tension forces are provided to illustrate the effectiveness, accuracy and robustness of the method.

Polypropylene engineered cementitious composites (PP-ECC) exhibit superior strength and strain hardening under tensile deformation, which is expected to enhance the anti-cracking performance and self-confinement of the plastic hinge region in structural columns. However, there is still a lack of fundamental studies on the compressive behavior of a reinforcement-confined PP-ECC column. This paper presents a proof-of-concept experimental study on the confined PP-ECC column and hybrid normal strength concrete (NSC)-ECC column. Two sets of reinforcement-confined columns were designed: a pure PP-ECC column and a hybrid C30-PP-ECC column. Then, static compression tests were carried out to prove the effectiveness of the confinement in enhancing the peak strength of the hybrid column with respect to pure PP-ECC columns. However, the deformability improvement was not remarkable, with an increase of only 3.2% from samples containing no stirrups to those containing stirrups at a volumetric ratio of 1.6%. An equation was proposed to predict the peak strength of the confined PP-ECC columns. This equation considered the contribution from the tensile capacity of PP-ECC to the circumferential confining effect of the columns. The hybrid column delivered better deformability but smaller peak strength compared with the pure PP-ECC columns. Some mechanical features of the hybrid column were discussed.

Natural rubber laminated bearings (NRBs) in sea-crossing or offshore bridges are extremely vulnerable to seawater dry-wet cycles due to weather conditions, wind, waves, and other factors in coastal areas. Seawater dry-wet cycles test was conducted on 20 NRBs and 63 rubber sheets for 60 days to investigate the influence of seawater dry-wet cycles on basic NRB performance. The change laws that govern the NRBs’ horizontal and vertical stiffness were obtained via seawater dry-wet cycles test. In addition, the proposed constitutive parameters of the rubber material were used to establish a finite-element model of the NRBs to simulate and analyze the bearings’ performance and time-varying law. The test results were then compared with the fitted and simulated results. Finally, the performance deterioration law of the NRBs was predicted over a 120-year lifespan based on the extrapolation of the 60-day test results, and the finite element analysis of the performance for NRB within 120-year service life was done to verify the reliable of the prediction result. The 60 days test results show that the NRBs’ horizontal and vertical stiffness increased by 23% and 7%, respectively, after test for 60 days, and horizontal and vertical stiffness increased linearly as the seawater dry-wet cycles test time increased. The findings presented in this paper lay a foundation for further research on the performance of NRBs and will play an important role in the study of the seismic resistance and life-cycle performance of sea-crossing bridges and other structures subjected to seawater dry-wet cycles.

Beam-column joint is one of the most vulnerable portions of a building during an earthquake. Sufficiently ductile materials are required to reinforce these joints so that the structure can dissipate energy and exhibit better performance during seismic events. Superelastic Shape Memory Alloys (SE SMAs) are unique materials that have the ability to undergo large inelastic deformation upon stress removal (superelasticity) or heating (shape-memory alloy effect). If such smart materials can be incorporated in the plastic hinge regions of reinforced concrete (RC) beam-column joint sub-assemblage, they can undergo large deformations without experiencing permanent deformation during an earthquake. In this context, this paper discusses the seismic performance of RC beam-column joint sub-assemblages reinforced with five different SMAs, obtained through numerical study, under reverse cyclic loading. In this study, six beam-column joint sub-assemblages, five reinforced with different types of SE SMAs, and one with regular steel, are considered. The performance of the beam-column joint sub-assemblages is numerically evaluated in terms of load-storey drift relationship, energy dissipation capacity, and cumulative energy dissipation-storey drift ratio. Nonlinear static pushover analysis is also carried out to determine the performance-based limit state for the beam-column joint sub-assemblages. The results indicate that all the SMA reinforced beam-column joint sub-assemblages have adequate energy dissipation capacity while experiencing lower residual deformation.

The objective of the present work is to analyse the ultimate strength of a tubular structure subjected to a bending moment. The tubular monopile structures are experimentally tested as well as the nonlinear finite element analysis is performed. Three specimens are designed for the experimental test by taking into consideration the typical ranges of the monopile support structures used in offshore wind turbines. The moment-curvature and the stress-strain relationship of the tested specimens are studied. The tested specimens are also evaluated numerically based on the finite element method employing a nonlinear FE analysis. The finite element analysis accounts for the nonlinearities associated with the geometry and material. The geometrical imperfections are introduced to the structure together with the initial stress arisen in the process of fabrication. The results obtained from the finite element analysis and the experimental tests are compared to each other and discussed.

Exterior walls and roofs in safety-related nuclear facilities in the United States, including nuclear power plants, must be designed to resist the loadings imposed by missiles (steel pipes, steel spheres, automobiles) borne by hurricanes and tornadoes. For confinement or containment, these walls and roofs are constructed from reinforced and/or prestressed concrete. The minimum required thicknesses of a reinforced panel to prevent scabbing and perforation for an impacting steel pipe are typically established using empirical formulae calibrated for rigid missiles and high velocities. To enable improved design of concrete panels to prevent scabbing and perforation by wind-borne steel pipes, numerical simulations were performed to: (1) investigate the effects of panel thickness, pipe mass and diameter, pipe velocity, and concrete uniaxial compressive and tensile strength on impact resistance, and (2) establish minimum panel thicknesses to prevent scabbing and perforation for the pipes and impact velocities specified in standards of practice. The numerical simulations used axisymmetric SPH models validated using data from tests at Sandia National Laboratory in the 1970s of four reinforced concrete panels impacted by Schedule 40 pipes. The values of panel thickness and concrete compressive strength considered in the parametric study are typical of those in existing nuclear power plant structures in the United States. The Schedule 40 pipe is the missile used for simulations because it is referenced in the United States Nuclear Regulatory Commission (USNRC) Standard Review Plan and the Department of Energy (DOE) Natural Phenomena Hazards Analysis and Design Criteria for DOE Facilities that point to Regulatory Guide (RG) 1.76, RG 1.221, and ANS-2.3. The impact velocities bound the maximum velocities recommended in the USNRC and ANS documents for design against the impact of Schedule 40 pipes. A considerable number of design parameters have a meaningful effect on the impact resistance of reinforced concrete panels but the most important, aside from panel thickness and impact velocity, is tensile strength of concrete. Results of the parametric study enable the writing of guidance on the minimum thickness of reinforced concrete panels to resist 152 mm (6 in), 203 mm (8 in) and 254 mm (10 in) diameter Schedule 40 pipes at impact velocities identified in RG 1.76, RG 1.221 and ANS-2.3. Panel thickness ranging from 305 mm (12 in) to 914 mm (36 in) are required to prevent perforation and scabbing caused by the impact of these Schedule 40 pipes. The required panel thickness decreases with increasing tensile strength.

In this article, a new family of two-stage explicit time integration methods is developed for more effective analyses of linear and nonlinear problems of structural dynamics. The collocation method and special types of difference approximations with adjustable algorithmic parameters are employed to approximate the displacement and velocity vectors in time. The new two-stage explicit method is designed to possess controllable numerical dissipation like many of the recent explicit methods. Interestingly, the period error of the new two-stage explicit method is noticeably decreased when compared with the existing two-stage explicit methods. All improved and preferable features of the new two-stage explicit method are achieved without additional computational costs. Illustrative linear and nonlinear problems are solved numerically by using the new and existing methods, and numerical results are carefully compared to verify the improved performance of the new two-stage explicit method.

Five full-scale reinforced concrete wall specimens with openings typical of the first story backside exterior walls of row houses in Taiwan were tested using lateral cyclic loading to study their seismic behavior. The effects of location and size of the window opening were studied. Test results showed that the wall with the window opening on the side of the wall web showed a higher average lateral strength than that with the opening placed around the center of the wall web. The increase of the opening length reduced more the lateral strength than the increase of the opening height. A critical wall segment tended to show a lower lateral strength when the edge of the segment is bordered by a door than by a boundary column. To estimate the lateral strength of the wall specimens, a detailed and three simplified models are proposed. Comparison with the test results shows that ignoring variation in the axial force among the wall segments and columns does not change the average prediction but increases the scatter of prediction. Simply summing the lateral strengths of all the wall segments and columns together further increases the scatter and greatly reduces the degree of conservatism. Summing the lateral strengths of all the web segments requires the least computational effort but greatly increases the degree of conservatism.

The application of performance-based design (PBD) is gaining increasing interest in the wind engineering community. A popular design approach to minimize wind induced vibrations in flexible civil structures is to size structural stiffness and supplemental damping systems in order to restrict the motion to a given threshold for providing safety and comfort, while ensuring that structural components meet strength requirements. In this paper the PBD paradigm is extended to wind excited tall buildings equipped with motion control systems. The objective is to improve the design of damping systems under different wind events while considering maximum acceleration as performance measure. In addition, since the installation of damping devices implies additional costs (e.g., installation and maintenance costs) while it helps decreasing the costs associated with performance failure, a life-cycle analysis (LCA) is integrated in the PBD. In the LCA framework, the percentage of building occupants affected by discomfort and motion sickness caused by excessive wind-induced vibrations is considered to account for the consequences of different target performance levels. The developed PBD is applied to a 39-story building that has documented issues with excessive vibrations under wind events. The wind load is simulated as a multivariate stochastic process, in the time domain. Two passive vibration mitigation strategies are investigated: viscous and friction dampers, both designed to meet the target performance levels. LCA are conducted for the building equipped with each damper type, and benchmarked against the one without dampers. Results show that the PBD leads to a rational and economically effective approach for the design of the damping systems in wind excited tall buildings.

In seismically active regions, the resistance of buildings against earthquakes must be improved. Post-installed anchors are generally used to connect retrofitting members to existing concrete members of a structure. However, research on the mechanical behavior of post-installed anchors subjected to combined shear and tensile stress is insufficient. Therefore, in this study, loading tests were conducted on anchor bolts by applying cyclic shear loading and constant tensile forces. Additionally, a mechanical model was constructed to evaluate the experimental results. In this model, the shear force was equal to the sum of the bending resistant force at the plastic hinge, the supporting stress of the concrete, and the shear component of the tensile stress of the anchor bolt. The results demonstrate that, with increasing tensile force, the shear force decreases and the joint separation increases. In addition, the proposed model was shown to reasonably replicate the shear load and slip relationship determined from experimentation results.