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The stress response behaviors of steel wires at the anchorage part of bridge cables under tension and bending coupling loads play a predominant role in determining their fatigue life and failure modes. The inherent complexity of the spiral geometry and the large diameter of actual bridge cables made the stress response behaviors of steel wires at the anchorage part unclear up to now. An analytical method was proposed for spiral steel wires at the anchorage part of semiparallel steel wire cables under tension and bending coupling loads. The corresponding refined numerical modeling method was also developed for studying the local anchorage part. Both the analytical formulation and numerical model agree well with the related experimental results in the literature. The presented analytical and numerical methods are thereby efficient and accurate to simulate bridge cables under tension and bending coupling loads. The critical slip curvature of steel wires increases linearly with the tensile strain of the bridge cable. The axial stresses of the steel wires of the bridge cable at a given longitudinal location display a linear relation with the angular change at the anchorage end. For steel wires located at the guide deviator part of the bridge cable, the axial stress behavior differs between the stick and slip states. It changes to a chord curve in the longitudinal direction in the stick state, while it follows an exponential function with respect to the polar angle in the slip state. The axial stress range of the outermost steel wire of the bridge cable increases linearly with the harmonic tension load range and the bending load range, separately. Regarding the phase difference between harmonic tension and bending coupling loads, a phase difference of 0 represents the most unfavorable combination for the bridge cable. By contrast, when the phase difference falls between 0 and π/2, the two harmonic loads tend to mutually inhibit each other's effects on the cable's behavior. [ABSTRACT FROM AUTHOR]

Glued-in rods are proficient and high-performance connectors, finding application in the construction of new timber edifices as well as retrofitting of pre-existing timber structures. Given the prevalence of high-rise timber constructions facilitated by the advent of cross-laminated timber (CLT), there exists an opportunity for the incorporation of glued-in rods in the connectivity solutions for these load-bearing structural elements. This study examines the empirical behavior of CLT connections employing multiple glued-in rods. To achieve this objective, comprehensive experiments were conducted, involving full-scale tests on specimens subjected to both monotonic and cyclic loading conditions. The investigation included variations in the embedment lengths of the rods (250 and 350 mm) as well as their orientations with respect to the wood grain (parallel, perpendicular, and interposed amid layers). The monotonic test results showed that glued-in rods embedded on the edge of the CLT could provide high-capacity connections. The angle at which the rod was oriented relative to the wood grain had an impact on both the failure mode and the shape of the force-displacement curve in the connections. To calculate the pull-out strength of the glued-in rods anchored in CLT, a design equation is proposed based on the shear strength of the bondline. Additionally, a comparative investigation was performed to study the effect of the reinforcement by screws on the connections strength under monotonic loading in tension and in compression. Moreover, it was observed that glued-in rod connections keep their elastic properties until failure under cyclic loading. The results obtained from this research exemplified that this specific connection type could present a reliable and sturdy option for use in CLT construction projects. [ABSTRACT FROM AUTHOR]

In order to study the influence of split grouting times on the anchorage performance of prestressed anchor cable, a field test of multisplit grouting was carried out using fiber Bragg grating monitoring technology. The ultimate bearing capacity, displacement, axial force, and shear stress distribution of the anchor cable under different split grouting times were studied. The test results show that (1) compared with conventional grouting methods, multiple split grouting can increase the bearing capacity of the anchor cable by two to three times, and the improvement effect is most obvious in secondary grouting; (2) the number of split grouts has no effect on the axial force of the anchorage section and does not change the shear stress distribution of the anchorage section. The axial and shear stresses of the anchor cable are mainly concentrated at the first 8 m of the anchorage section. With the increasing tension load, debonding and sliding will occur at the front of the anchorage section, and the peak shear stress will move to the depth of the anchorage section. (3) When the anchor cable fails, the total displacement increases with the increase in splitting and grouting times. The conventional grouting anchor cable begins to produce plastic displacement early, while the plastic displacement of the split grouting anchor cable occurs when the external load is close to the failure load. (4) The multiple high-pressure split grouting technology is applicable to the reinforcement of foundation pits or slope engineering and is a valuable support and reinforcement technology. [ABSTRACT FROM AUTHOR]

Chalk is encountered under large areas of Northern Europe and other locations worldwide, and a wide range of onshore and offshore structures are founded on piles driven in chalk. The safe and economical design of these structures is challenging because of current uncertainties regarding their axial capacity and load-displacement behavior. This work builds on recent research into the axial capacity of open-ended driven piles by proposing new shaft and base load transfer models for chalk that employ geotechnical properties measured directly in laboratory and in-situ tests. First, this study set out a new closed-form elastic analysis of the initial tension loading response. Then, a new nonlinear shaft model was proposed that captures the radial variation in properties induced by pile installation in chalk and uncouples the piles' stiffness responses from their ultimate local shaft resistances, which are predicted independently. A new base model was also outlined that predicts the loading response based on the chalk's small-strain stiffness and cone penetration test (CPT) cone resistances. The models are shown to offer good load-displacement predictions for 0.139-m to 1.8-m diameter piles tested between 20 and 600 days after driving at several sites. Improved reliability and accuracy are demonstrated through comparison with existing load-transfer methods. [ABSTRACT FROM AUTHOR]

A new connection joint between precast concrete bridge slabs, headed bar joints in high-performance fiber-reinforced mortar (HPFRM), is proposed to reduce the lap length and simplify the construction process of the traditional slab joint configurations. To investigate the tensile behavior of the proposed headed bar joints in HPFRM between precast concrete bridge slabs, four groups of 12-headed bar joint specimens were tested in different loading rules. Contributing factors to the joint tensile strength, including anchor plate configurations and loading rules, were investigated. A three-dimensional refined rib-scale finite-element (FE) modeling method was further proposed and verified against the experimental results. The working mechanism of mechanical anchorage and indirect lap splice was analyzed based on the FE analysis. This research shows that with the reinforcing bar spacing and lap length used in this paper, the joint specimens having 60 mm or less anchor plate length encountered conical shear failure before the rebars reached the characteristic tensile strength. At the peak load, with the degradation of the bond between reinforcement and mortar, the coworking mechanism of the mechanical anchorage and bond was switched to mechanical anchorage alone carrying most of the applied load. Increasing the anchor plate thickness can effectively improve the tensile stiffness and strength of the joint and hence avoid conical shear failure, while the influence of loading rules is very limited. The proposed refined rib-scale model can accurately predict the failure mode and tensile strength of the headed bar joints without artificially assuming the bond–slip constitutive relationship. [ABSTRACT FROM AUTHOR]

This study examines the capacity of single piles subjected to cyclic axial tension or compression load in the loess area under in situ compaction degree and extruding conditions. Four cyclic tension and compression loading tests, and two conventional tension and compression tests on single piles were carried out at a typical loess site of the Loess Plateau region of Northwest China's Shaanxi Province. A series of pretest preparations, including site leveling, steel cage production, pile formation, and soil compaction, are performed. The axial displacement of pile top, pile axial force, and frictional force of the pile side of a single pile measured in the test process were analyzed. The cyclic tension or compression load–displacement curves of the piles in loess, under the in situ compaction degree condition, show the load results in an influence of the movement trend that cannot be ignored. There is no overlap between the compression-unloading curve and tension-unloading curve. This phenomenon indicates that the cyclic loading accelerates the destruction of the pile foundation. Under an extruding condition, the difference between the maximum deformation and the minimum deformation is 2.412 mm, which is 60% of the ultimate deformation of a conventional single pile. The lateral friction of the pile shows multipeak distribution along the pile body, and the attenuation range of lateral friction strength at the pile tip is more than 50% in the failure stage. [ABSTRACT FROM AUTHOR]

In this study, cyclic tension tests were conducted on ordinary Galfan cables and locked coil Galfan cables with diameters of 40 mm to evaluate their mechanical properties under cyclic tension. The mechanical behavior of the two kinds of Galfan cables under monotonic loading and cyclic tension was analyzed, while the differences in strength and the mechanical properties of the two kinds of Galfan cables and the effects of different loading systems on the mechanical properties of the two kinds of cables were obtained. The Ramberg–Osgood model was used to fit the skeleton curve. The elastic and inelastic behaviors during loading and unloading were studied. The change in elastic modulus of the Galfan cable with respect to cyclic load is proposed, and the exponential model of strain and elastic modulus under cyclic load is established, which lays a foundation for the accurate finite element analysis of cable structure response under strong earthquake and other accidental loads. [ABSTRACT FROM AUTHOR]

Most research on circular hollow section (CHS) flange-plate connections deals with axial tension loading, yet bending action is a common load case. Prior researchers have studied both ring and blank-flange-plate connections, using a four-point-bending setup, generating a database of 10 experimental tests and five numerical models on bolted blank-flange-plate connections under pure bending. This limited data is extended herein by two large-scale laboratory tests with blank-flange-plate connections having a large span-to-tube diameter ratio, and 120 numerical models. Flange-plate plastification and bolt fracture are the valid failure modes for this splice, so all data was meticulously assessed to exclude experimental tests or numerical models not governed by connection failure. Existing design models for calculating the connection capacity under pure bending are evaluated and revised. Moreover, based on rectangular flange-plate connections, a novel method is proposed to design its circular counterpart under pure bending. For all methods, the difference in using the ultimate stress for flange-plate moment capacity—instead of the conventional yield stress—is also analyzed. Lastly, a reliability analysis is conducted to support the proposed design method. [ABSTRACT FROM AUTHOR]

This study entailed axial cyclic loading tests conducted on full-scale diagonal tension members of steel deck-truss bridges to evaluate the effects of seismic retrofitting methods using carbon fiber–reinforced polymer (CFRP) sheets. The loading tests were performed on CFRP-retrofitted specimens with varying anchoring lengths of the CFRP sheets. The results indicated that the proposed retrofitting methods, which employed the intermediate-modulus CFRP type (390–450 GPa) and polyurea putty (a ductile adhesive), delayed the plastic buckling of the flanges and substantially increased the load-carrying capacities, stiffnesses, and ductility capacities of the retrofitted diagonal tension members. Additionally, the polyurea putty effectively suppressed the peeling failure of the CFRP sheets. It maintained the cross-sectional integrity between the steel members and CFRP sheets even after the plastic buckling of the flanges and rupture failure of the CFRP sheets. Further, finite-element analyses accurately reproduced the loading test results by considering the nonlinear bond-slip performance of polyurea putty, anisotropic characteristics of the CFRP sheets, and cyclic plasticity properties of steel. [ABSTRACT FROM AUTHOR]

High pressure and high temperature (HPHT) oil and gas pipelines, the burial depths of which are determined by the mitigation requirement of upheaval buckling deformation or legislation requirement, are commonly buried below the ground surface. Uplift resistance of soils surrounding the buried pipeline should be considered into the design of upheaval buckling behavior. Conventional design guidelines and current analytical models based on either dry soil or fully saturated soil are generally applied to predict the soil uplift resistance behavior. Therefore, the HPHT pipelines are mostly buried in unsaturated onshore soils. This paper presents a series of small pipe–soil interaction experiments for measuring the reaction that is acted on the buried pipelines in unsaturated backfill soils, and its purpose is studied to evaluate the impacts of soil moisture content, pipeline burial depths, and tension loading levels on the soil uplift resistance behavior. A new simplified formula based on the uplift experiment results is specially established to predict the uplift resistance of soils. Further, the uplift failure mechanism and pipe–soil interaction behavior are effectively applied to predict the upheaval buckling behavior of the pipelines buried in unsaturated soils. [ABSTRACT FROM AUTHOR]

In this study, a mesh-independent fracture model is implemented in the standard finite-element (FE) framework by leveraging a volume averaging approach. For the tension regime, a cohesive crack model is adopted for the onset and propagation of the crack, in which the direction of a new crack is defined as the eigenvector of the maximum principal stress. For the compression regime, the Coulomb criterion is considered for the onset and propagation of the crack, and the new crack direction is obtained based on the Mohr–Coulomb criterion by employing the residual friction angle. In addition, a new return mapping algorithm, i.e., the general return mapping, is developed for both compression and tension loading conditions to improve the numerical robustness, convergence, and accuracy. Finally, in order to validate the constitutive behavior, a stress-point calculation is performed, followed by boundary value problems to illustrate the robustness of the suggested return mapping algorithms and the mesh-independence effects of the volume averaging methodology. [ABSTRACT FROM AUTHOR]

The particle-scale shear and tensile strength measurements of microbial-induced calcite precipitation (MICP) treatment have been investigated in this paper. Glass beads were used to represent sand particles. Three particle-scale test setups were developed to measure the tensile, shear, and cyclic shear strength of MICP-treated CaCO3 bonds between glass beads. Sporosarcina pasteurii bacterial cells were introduced to precipitate CaCO3 and form cementation bonds between glass beads. The preliminary particle-scale test (Test setup 1) was designed to measure the shear and tensile strength of CaCO3 bonds precipitated between glass beads mounted on optical fiber sensors with known properties. Shear and tension loads were applied to the CaCO3 bonds by the displacement actuators controlling the movement of movable stages. The improved particle-scale test setup (Test setup 2) was developed using a larger and stable reaction chamber, an automated injecting system, and stiff bending elements (instead of optical fibers) that were connected to glass beads to improve measurements. Deflections of the bending elements were measured to calculate the tensile and shear strength of the CaCO3 bonds using the beam theory. The enhanced particle-scale test setup (Test setup 3) was developed to directly measure the shear and tensile forces generated in CaCO3 bonds using load cells and LVDTs to investigate the monotonic and cyclic response of the CaCO3 bonds. For the tests using Test setup 3, the shear and tensile strengths were 378 and 446 kPa, respectively. [ABSTRACT FROM AUTHOR]

Toothed metal-plate connector (MPC) is a cost-effective connection method, easy to install with high assembly efficiency for manufacturing engineered timber trusses. In this study, In order to combine the advantages of the MPC with glued laminated bamboo (glubam) structures, a total of 136 MPC glubam joints, divided into 22 groups according to testing parameters, were tested and analyzed. Design strength values of the anchorage strength of metal plate tooth embedded in glubam, the tensile and shear strengths of toothed metal plate in glubam joints were provided in reference of the existing timber code specifications. The results show that the linear interpolation formula provided by the existing design code largely overestimates the anchorage strength of metal plate tooth embedded in glubam for the nonorthogonal loading directions. An angular equation expressed as the loading direction is therefore proposed. The design shear strength of aligning the major axis (tooth slot direction) of the metal plate parallel to the plate longitudinal direction is higher than that of aligning plate major axis perpendicular to the plate longitudinal direction, especially for the combined shear and tension loading. The design tensile and shear strengths of the MPC glubam joints are obviously larger than those of the Class I MPC timber joints given in the Chinese Standard, indicating that the MPC glubam is hopeful to be alternative to replace the MPC timber structures such as roof truss systems. [ABSTRACT FROM AUTHOR]

With the rapid development of transmission-line engineering in western China and the frequent occurrence of extreme natural disasters, a great deal of attention has been paid to the bearing capacity of foundation systems. The uplift capacity is still the controlling factor in the design, but neglecting the horizontal load component will induce great potential risks to the stability of the foundation. This paper describes the model test of rock-socketed piles (with soil overlying rock) that were subjected to axial and oblique tension impacts. Furthermore, the load displacement response, failure mode, and load transfer mechanism of the model piles were compared and discussed. The research indicates that the uplift capacity of the model pile under the oblique load can be remarkably reduced by up to 27.3% in comparison with the vertical uplift. Moreover, the load–displacement curve of the model pile under axial and oblique loads present abrupt failure. Notably, the failure mode under the axial tension is an inverted cone-shaped axisymmetric failure, and the failure mode under the oblique tension shows the wedge failure on the compression side and the interface separation on the tension side. The compression side and tension side show the opposite load transfer mechanism, thus inducing the presence of a bending moment in oblique tension pile. The position of the maximum bending moment occurs at the depth of 2.3–2.8d below ground surface. In summary, the research results of this paper have important guiding significance for design of transmission tower foundation in similar geological settings. [ABSTRACT FROM AUTHOR]

This paper presents a novel anchorage structure for stay cables to reduce the load on the concrete pylon. Called the staggered-supported steel anchor box (SS-SAB), this anchorage structure provides self-balancing of the horizontal component of the cable tension force during cable tensioning; the vertical load is transferred to the concrete pylon through a staggered support. The SS-SAB can tolerate the forces within the spatial cable plane and reduce the cracking risks of the concrete pylon. To investigate the behavior of the SS-SAB, a half-scale specimen was designed and tested. Data on the deformation, crack patterns, local strains, and slippages were obtained that demonstrate that the SS-SAB can delay crack occurrences in the concrete pylon. In a supplementary analysis, a finite-element analysis performed using the ABAQUS software suite delivered good accuracy. From the test and numerical analysis, the influence of the cable angle on load sharing within the concrete pylon was investigated. The effective scope of applications of the SS-SAB is provided. [ABSTRACT FROM AUTHOR]

This paper presents the behavior of amorphous metallic fiber (AMF)–reinforced geopolymer composites under compression, bending, and uniaxial tension loads. Comparison is also made with counterpart cement composites reinforced by AMF and steel fiber (SF)–reinforced geopolymer composites. In this study four series of composites were considered in two parts. In the first part, heat cured geopolymer (HCG) composites reinforced by 0.5%, 1.0%, and 1.5% (by volume) AMF were considered in one series, while similar volume fractions of AMF were used to reinforce conventional cement composite in another series to benchmark the observed properties. In the second part, similar volume fractions of AMF were used to reinforce ambient air cured geopolymer (ACG) composites, and the results were benchmarked with conventional SF-reinforced ACG composites. The water to cement ratio and alkali activator to binder ratios in all composites were kept constant for comparison, and all composites were tested after 28 days of curing. The results showed that the compressive strength of AMF-reinforced HCG composites was higher than that of AMF-reinforced cement and AMF-reinforced ACG composites. However, the compressive strength of SF-reinforced cement composites was slightly higher than that of AMF-reinforced ACG composites. Regardless of composite and fiber types, an increasing trend in compressive strength with an increase in the volume fraction of fibers was also observed. The results also showed higher flexural and tensile strengths for AMF-reinforced HCG composites than for counterpart cement composites. The flexural and tensile strengths of both geopolymer composites also increased with an increase in AMF volume fraction. However, both flexural and tensile strengths were higher for ACG composites when reinforced by SF than when reinforced by AMF. Microstructural observations through scanning electron microscopy showed no damage of the AMF and SF in the geopolymer composites and showed higher amounts of geopolymer matrix on the surface of AMF in HCG composites than in cement and ACG composites. [ABSTRACT FROM AUTHOR]

This research experimentally investigated the applicability of glass fiber–reinforced polymer (GFRP) bars as postinstalled reinforcement in structural connections. The test specimens included two identical vertical elements, which were anchored into a reinforced concrete base using postinstalled GFRP bars replicating a beam–column or beam–wall connection. The variables investigated included the GFRP bar embedment depth (150 and 290 mm), concrete compressive strength (20.7 and 41.4 MPa), and postinstalled GFRP bar size (Nos. 13, 19, or 25). A total of 16 specimens were subjected to combined tension and shear loading. Concrete breakout in tension was the failure mode in all specimens. The concrete breakout strengths improved by increasing the embedment depths and concrete strengths and worsened as the GFRP bar diameter increased while keeping the embedment depth and concrete strength constant. The authors recommend using anchor provisions from current standards to estimate the concrete breakout strength of post-installed GFRP bars (Nos. 13–19) tested with the parameters described herein. [ABSTRACT FROM AUTHOR]

This paper presents the field test results for 3.3-m-long driven steel pipe single vertical piles, P1 (β=0°) , and single batter piles, P2 (β=10°) and P3 (β=20°) , for four different eccentric moments (W·e=0.225 , 0,885, 1.454, and 1.944 N·m) under the static load (Ws) of 12 kN and 14 kN subjected to horizontal excitation acting both in the direction and transverse to the direction of pile batter. The field test results include the frequency-amplitude response, soil-pile separation length, distribution of dynamic bending moment, and dynamic axial load. The observed frequency-amplitude responses displayed nonlinearity in both the horizontal and rocking components of motion for all the piles. It was ascertained that with the increase in the pile batter angle, the resonant frequency increases, and resonant amplitude decreases. The test results also showed that batter piles generate lesser dynamic bending moment and higher dynamic axial load along the pile than the vertical pile. The frequency-amplitude responses from the field tests were compared with the theoretical prediction based on the continuum approach. It was found that the continuum approach with precise boundary zone parameters predicted the dynamic response of all the piles reasonably well in comparison to the dynamic field test results. It has been observed that the batter piles with loading direction in the direction of pile batter generate a substantial increase in the horizontal and rocking stiffness as compared to the batter piles with loading direction transverse to the direction of pile batter. Furthermore, the study highlights the normalized plots on the effect of pile batter angle, loading direction, eccentric moment, and static load on resonant frequency and resonant amplitude based on the theoretical and experimental studies. [ABSTRACT FROM AUTHOR]

Load and resistance factor design (LRFD) for serviceability limit state (SLS) of laterally loaded drilled shafts was explored for transmission line structures in sand, and the SLS resistance factor (RF) was proposed. Statistical characteristics of various load components, including transverse tension load (TTL), wind-on-structure load (WSL), and wind-on-conductor load (WCL), were considered and assessed. A database was established and adopted to calibrate RF for SLS of laterally loaded drilled shafts in sands. The hyperbolic model was introduced to quantify uncertainties in the lateral load–displacement curves for drilled shafts and adopted to determine the allowable load capacity. A Monte Carlo simulation was performed to calibrate RF for SLS. The effects of target reliability index (βT), allowable displacement (ya), ice thickness on conductor (Iz), and various load ratios were all considered in the RF calibration. The values of RF for SLS varied from 0.19 to 0.94 for βT in the range of 1.5–3.5. Equivalent factors of safety (FSeq) were obtained for the proposed RFs to evaluate and compare the safety margin of SLS to that of current design practice. [ABSTRACT FROM AUTHOR]

A one-dimensional technical theory for pretwisted isotropic linearly elastic beams loaded in tension and torsion was developed. The analysis was based on a kinematically admissible field written in terms of three generalized displacements, which were determined from the theorem of minimum potential energy. A general analytical solution was developed. The problem of a pretwisted beam with a built-in end and loaded in tension and torsion at the other end was analyzed. The problem also was solved by carrying out detailed three-dimensional finite-element calculations. The predictions of the technical theory agreed very well with the results of the finite-element solution. The effects of Poisson's ratio were examined, and the applicability of the model to beams of various lengths was discussed. [ABSTRACT FROM AUTHOR]

The uniform arrangement of pile groups widely used in practice often causes obvious differential settlement of pile foundations. To decrease differential settlement of pile groups, individual piles nonuniformly arranged can be adopted. This paper presents a model test study on the bearing capacity of pile foundations under different pile arrangements. A versatile full-automatic loading system and data acquisition and analysis systems of the model test were developed. Using the model test setup, the response of a single pile subjected to axial load was clarified, and the reinforcing effect between an axially loaded pile and a load-free pile was then analyzed. Furthermore, model tests were carried out to assess the behavior of the pile groups composed of individual piles with variable length and diameter. For practical purposes, some suggestions on the nonuniformly arranged individual piles within pile groups were given to decrease differential settlement among each individual pile and make maximum use of the bearing capacity of each individual pile. [ABSTRACT FROM AUTHOR]

In this study, the resistance factors (RF) in the load and resistance factor design (LRFD) for the drilled-shaft foundation of transmission line structures subjected to lateral loads were investigated. Various load test results were collected to establish a database and used in the reliability analysis. The first-order reliability method (FORM) was implemented to calibrate RF for the Broms, Brinch-Hansen, and Prasad and Chari methods. Loads for transmission line structures were categorized and characterized statistically for calibrating RF. Uncertainties of the transverse tension load (TTL), wind-on-structure load (WLs), and wind-on-ice-coated conductor load (WLc), all dominant in transmission line structures, were evaluated. RF varied largely with nominal load ratios of WLs/TTL and WLc/TTL , which should be considered for the selection of RF in the design to maintain a consistent safety margin. Increases in nominal WLs and WLc induced higher RF while increasing nominal TTL yielded lower RF. The higher RF values obtained in this study were due to the low bias factors of wind-induced loads and the large load factors of the tension and wind loads. The equivalent factor of safety (FSeq) was evaluated and analyzed for the proposed RF s. [ABSTRACT FROM AUTHOR]

In recent years, there has been a significant push to develop optimized pile designs in the offshore industry, driven by the growth of offshore wind. One of the largest remaining uncertainties governing axial pile design in sands is the influence of ageing effects and how an aged pile responds under axial cyclic loading. This paper presents results from a long-term campaign of field tests on pile ageing and axial cyclic loading in sands, undertaken at the Blessington geotechnical test site in Ireland. Five open-ended driven steel piles were subjected to a total of 33 static and cyclic tension pile load tests undertaken over a 3-year period. The tests were planned and coordinated in order to accurately quantify the effects of ageing and cyclic loading on the pile shaft capacity over time. The tests showed that significant gains in pile shaft capacity occurred over time as a result of pile ageing, in line with results presented by other researchers. Piles subjected to cyclic tension loading remained stable under cyclic loading at load levels much larger than their 1-day capacity. The 1-day capacity appears to offer a lower bound for the degraded pile capacity following tension cyclic loading to failure. The reduction in capacity caused by cyclic loading to failure was related to the pretest increase in capacity caused by ageing. The findings from these field tests in addition to reinterpretation of previous testing indicated that previously published cyclic interaction boundaries may be overly conservative. [ABSTRACT FROM AUTHOR]

The development of strong and stiff lateral load-resisting systems (LLRS) is essential for mid-rise and high-rise timber buildings. On the other hand, within a seismic design philosophy, strength/stiffness and ductility/drift capacity typically appear as opposite target parameters, depending on the acceptable level of damage. For improved stiffness and strength, core-wall tubular structural forms commonly are used for taller reinforced concrete (RC) buildings. This paper presents an experimental study of a new type of LLRS in cross-laminated timber (CLT). A post-tensioned C-shaped CLT core-wall mainly using screwed connections was designed and tested under unidirectional and bidirectional cyclic loading. It was found that the mixed-angle screwed connection solution was the most effective. The highest partial composite action of 60%–70% was reached and the core-wall system stiffness at serviceability limit state increased more than four times compared with a decoupled test with only friction between the CLT panels. The (unbonded) post-tensioning technology provided strong and stiff core-wall base connections with recentering capability and small residual displacements. The experimental test results confirmed that significant system strength/stiffness and ductility/drift capacity can be achieved in a post-tensioned C-shaped CLT core-wall system with minimal damage through careful connection detailing. [ABSTRACT FROM AUTHOR]

A total of 105 cross-tension tests were conducted to investigate the strength and behavior of power-actuated fastener (PAF) connections under quasi-static monotonic tensile loading. Three types of PAF were used to join sheets with thicknesses ranging from 0.75 to 4.00 mm to thicker plates with thicknesses ranging from 3.00 to 20.0 mm. All of the steel materials were high-strength cold-formed steel, except for the 20-mm-thick steel, which was hot-rolled steel. The studied parameters were the type and diameter of the fasteners and the thicknesses of the top and base steel materials. The majority of the specimens failed by pull-out failure, although some thinner sheets failed by transverse fracture of the top sheet. The test results reveal that PAF connections exhibit a high tensile capacity as long as a sufficient embedment length is provided. A model is proposed to evaluate the pull-out strength of PAF connections based on the base material strength and the average embedded diameter and embedment length of the fastener. The proposed model produces a mean of test-to-prediction ratio equal to 1.02 with a coefficient of variation ranging from 0.12 to 0.16. Reliability analyses were carried out and resulted in a resistance factor of 0.56–0.69 for Load and Resistance Factor Design. [ABSTRACT FROM AUTHOR]

Interface friction is a governing parameter in the performance of piled foundations and other applications. Piles and other foundation elements typically mobilize a similar interface friction angle during loading in tension and compression. However, some applications may benefit from surfaces that mobilize higher shear resistance in one direction of loading relative to another. Such behavior can be achieved through inspiration from the underbelly scales of snakes, which produce frictional directionality or anisotropy. This paper presents the results of an experimental investigation on the monotonic and cyclic interface shear behavior of snakeskin-inspired surfaces and piles with sand. Laboratory test results provide evidence that snakeskin-inspired surfaces mobilize shear resistance, volumetric behavior, and strength degradation that depend on the shearing direction. Boundary conditions, sand relative density, and cyclic displacement amplitude are also indicated to influence the interface shear response. Centrifuge pile load tests are used to evaluate the installation forces, pullout capacity, and cyclic loading response mobilized by snakeskin-inspired piles. These results suggest that snakeskin-inspired surfaces can readily mobilize skin friction that depends on the direction of the displacement in piling applications. [ABSTRACT FROM AUTHOR]

This paper presents full-scale field tests of grouted steel pipe micropile embedded in marine soft clay under compressive and tensile loads. The load-displacement responses, axial forces, tip resistance, and unit skin friction were measured and evaluated. The relationship between skin friction and pile–soil relative displacement in each soil layer is discussed. The bearing capacity of the micropile was improved by the post-grouting technique. After post-grouting, the ultimate skin friction of the soft clay under compression and tension was improved by 48.7% and 30.8%, respectively. The ultimate bearing capacity of the grouted steel pipe micropile under a compression load is approximately twice that under a tension load. [ABSTRACT FROM AUTHOR]

Four shear-critical RC shear walls were tested under a tension-bending-shear load to replicate seismic behavior of the bottom shear wall in high-rise buildings. The axial tension ratio ranged from 0 to 0.5 and the aspect ratio was 1.06. The shear compression failure mode was observed for each specimen, characterized by the formation of an inclined crack at 45° and direct strut action. The shear displacement was a dominant deformation component throughout the loading history. When the axial tension force increased from 0 to 1,293 kN, the ultimate drift ratio increased from 0.90% to 2.38%, while shear capacity linearly decreased from 1,507 to 895 kN. The load–displacement curve showed a significant pinching effect and strength degradation effect. In addition, this paper reports an innovative experimental method to obtain shear resistance of transverse reinforcement (Vs) based on the plasticity theory and strain measuring result. Test results using this method show that not all horizontal distributed rebar yield simultaneously at the ultimate capacity. The US code-specified shear strength contribution of horizontal distributed rebar was found to be unsafe for each test specimen. Finally, a database of RC shear walls subject to combined tension-bending-shear load was established to evaluate shear strength formulas in design codes. The comparison showed the Chinese code predicted spuriously higher tension-shear capacity, while the US code predicted conservative capacity. Based on the developed database, a simplified design formula is proposed with adequate safety concerns and accuracy. [ABSTRACT FROM AUTHOR]

Concrete walls are used commonly as part of the lateral-load resisting system for buildings in regions of high seismicity. Damage to walled buildings in recent earthquakes has highlighted the seismic vulnerability of these systems. In recent years, most research addressing the seismic design of walls has employed experimental testing and focused on detailing of boundary element reinforcement to improve wall deformability. The research presented here employs numerical modeling and focuses on determining appropriate moment and shear demands for use in design. Previous research by the authors employed experimental data to develop a computationally efficient model that provides accurate simulation of flexural wall response, including compression- and tension-controlled flexural failure modes that have been observed in the laboratory and field. The research presented here used this model to develop validated expressions of the shear demand and the moment envelope. To do so, the earthquake response of idealized walled buildings, ranging in height from six to thirty stories,was numerically simulated. Initially, a series of walled buildings was designed using current U.S. code requirements, with moment and shear demands determined using both the equivalent lateral force (ELF) procedure and elastic modal response spectrum analysis (MRSA). Nonlinear dynamic analyses of these code-compliant buildings were conducted using a set of far-field ground motions scaled to various intensity levels. The results of the nonlinear analyses indicated the shear demands developed during earthquake loading exceed the design demands that were calculated using the elastic analysis methods. This could be expected to result in walls developing undesirable failure modes and exhibiting reduced deformation capacity. Because nonlinear analysis is not practical for design of many walled buildings, the nonlinear analysis results were used to (1) develop new procedures for determining the seismic shear demand to ensure flexure-controlled response and (2) identify moment envelopes for use in design that ensure flexural yielding is isolated to locations identified by the engineer. A suite of walled buildings was designed using the new recommendations. Analyses show that use of these new procedures results in a shear demand/ capacity ratio less than 1 and controlled flexural hinging. In addition, the response modification coefficients (i.e., R-factors) were revisited; the results show that lower R-factors are needed for walled buildings with planar or asymmetric walls to achieve acceptable collapse risk. [ABSTRACT FROM AUTHOR]

In a spirit of adventure, a boring was made and soil moisture contents measured along a tension crack near the crest of an earth embankment. Moisture contents increased linearly with depth and then sharply decreased at what is interpreted to be the bottom of the crack. Desiccation does not appear to have been a factor because of construction delays due to rains as the embankment still was under construction. It is hypothesized that the crack was created by quasi-elastic rebound of the recently compacted soil directed normal to the intersecting ground surfaces. A second increase in moisture content that appears to be linear with depth was discovered as the boring had been extended all of the way through to the bottom of the embankment. This change in moisture contents suggests a possible basal crack that can be attributed to differential settlement, and is assumed to connect to the upper crack as it was encountered in the same boring. Hydraulic connection may have been impaired by pinching action related to differential settlement but still could allow some water to go through. A comparison of the two mechanisms suggests that the upper crack probably formed first. A basal crack that remains open should be relevant for earth dams. [ABSTRACT FROM AUTHOR]

A variety of structures similar tomarine dolphins, dock-fendering systems, tower foundations, inundated platforms, and abutments are installed on deep foundations, which are subjected to uplift loads. This paper introduces a modern pile-modification strategy known as finned pile that increases pile-tension capacity by providing an affirmative anchorage close to the pile tip. The alteration consists of four fins welded at the bottom of a pile around the circumferential area. Comparative small-scale model uplift tests were performed on normal piles without fins and on piles with fins. Investigations were done by changing the fin-width ratio (b/D), fin inclination angle (β), pile length-todiameter ratio (L/D), and soil density. Results indicate that there is a considerable increase in uplift capacity of the piles when using fins at the end of the piles. When fins were installed with effective width equal to the pile diameter and at an inclination angle (β) of 90° for sand, with relative density (Dr) of 50%, the improvement in uplift capacity reached 1.82, 3, and 6 times that of the normal pile with L/D stiffnesses of 15, 20, and 30, respectively. It was also found that fins should be installed with an optimum fin inclination angle (β) equal to or greater than 45° to achieve the beneficial effect. The existence of such fins at the lower part of the tested piles provided an ideal anchorage system because of the significant locking-up effect of the soils within the fins, resulting in increased uplift capacity. [ABSTRACT FROM AUTHOR]

The mechanical properties of a polyurethane-cement hybrid foam are investigated. The hybrid foam, based on the combined, synergic use of rigid polyurethane foam and portland cement, was introduced for application in the building field. Thermal and acoustic insulation properties, water vapor permeability, and the fire resistance of the material have been reported in previous works. Here, a broad mechanical characterization including compressive, tensile, and shear tests is conducted according to ASTM standard methods for cellular plastic materials. The compressive tests show a brittle behavior of the hybrid foam, with the maximum strength achieved at large values of strain, compared to concrete. The material exhibits more strength under tension than under compression. The shear resistance values are similar to those of other building materials generally used for nonstructural components, i.e., cellular concrete and bricks. Finally, by comparing the physical properties of the hybrid foam with those of bricks and cellular concrete it is possible to highlight that the lightweight features of the former, associated with appreciable mechanical properties, make it suitable for building nonstructural components, also in seismic zones. [ABSTRACT FROM AUTHOR]

This paper describes an experimental investigation on the resistance and failure mode of four precast concrete frames. Each frame comprised a middle beam-column joint, a double-span beam, and two side columns. Two parameters, namely, reinforcement detailing in the beam-column joint and dimensions of the side columns, were investigated in the experimental program. Frame specimens were loaded on the middle joint by a vertical servohydraulic actuator, and corresponding horizontal reaction forces were recorded through load cells connected to the side columns. Experimental results and observations indicate that precast concrete frames were capable of developing compressive arch action (CAA) at the initial loading stage. However, frames with smaller side columns exhibited shear failure in the side joint. This hindered the development of catenary action in the bridging beam. By increasing the dimensions of the side columns, significant catenary action developed in the frames, and eventually flexural failure of the side columns took place resulting from horizontal tension force from the bridging beam. Experimental results suggest that horizontal forces induced by CAA and catenary action in the bridging beam have to be considered in the design of side columns and beam-column joints against progressive collapse. [ABSTRACT FROM AUTHOR]

To support the repair and maintenance of steel eyebars in bridges, tension stresses are sometimes estimated from the observed member natural frequencies. Although the ends of such eyebars are often essentially fixed, a pin-ended model has typically been used to predict tensions because closed-form solutions do not exist for any other end conditions. An approximation that reflects vibrating stretched wires with fixed ends has also been used, but this still incurs considerable error at lower member slenderness and stress levels. To provide for better estimates of eyebar tensions from observed vibrations, this paper presents exact tabular solutions for determining the direct tension stress in undamped steel bars, generalized for any length or thickness, where both ends of the member are fixed or where one end is fixed and the other pinned. Approximation equations derived from these exact solutions are also developed. Examples demonstrate the application of these new tools and the potential increase in accuracy over the former methods. [ABSTRACT FROM AUTHOR]

The indirect Brazilian test is widely used in engineering practice to indirectly determine the tensile strength of concrete. The Brazilian test (splitting tension test) is performed by applying a concentrated compressive load across the diameter of a disc-specimen. A series of dynamic Brazilian disc tests for concrete specimens were conducted using the split Hopkinson pressure bar (SHPB) technique. The objective of this paper is to investigate the standard Brazilian test by comparing the results obtained using the test with those obtained using a loaded arc, together with a comparison of the experimental results and the statistical analysis. The effect of loading angle on the dynamic splitting tensile strength was studied by one-way analysis of variance. By using linear regression method, the Weibull statistical model was introduced to obtain the relationship between the loading angle and dynamic splitting tensile strength of concrete. It was concluded that dynamic tensile strength of concrete is strongly dependent on the type of jaws. A general increase in failure load was obtained with an increasing angle of loading arc for all specimens tested. With an increase of loading angle, the Weibull parameters increase. The Weibull statistical model can describe the distribution law of the dynamic tensile strength of concrete. [ABSTRACT FROM AUTHOR]

Even at first loading, restrained shrinkage of concrete might significantly affect cracking resistance and short-term deformations. Correct assessment of this effect is of vital importance in constitutive analysis. Recently the authors proposed a methodology for eliminating the shrinkage effect from short-term moment-curvature and tension stiffening relationships. However, owing to rather complex issues of convergence and numerical integration, this approach was difficult to apply in practice. The present study proposes an improvement making the methodology a transparent and mechanically sound tool for analysis. The key strategy for the modification was to reduce a large number of concrete layers to two layers, one tensile and one compressive, the latter being assumed to be linear elastic. The study introduces a new concept of tension stiffening, the hybrid model, combining features of the reinforcement-related and the concrete-related approaches. Like the reinforcement-related approach, it assumes that tension stiffening stresses act in the same area in which tensile reinforcement occurs. To account for the shrinkage effect, tension stiffening is related to the concrete—a material capable of shrinking. [ABSTRACT FROM AUTHOR]

Experimental observations were made for the shear capacity of reinforced concrete beams with carbon fiber-reinforced polymer rectangular stirrups (CFRPRS). In total, 12 concrete beams were tested under three-point loading. Each beam measured 1,400 mm long, 150 mm wide, and 250 mm deep. For comparative studies, different parameters were considered: different sectional shapes (circular and rectangular CFRP stirrups), material types (steel and CFRP), and reinforcement ratios of stirrups (0.0038 and 0.0096). All beams were subjected to three-point loading. Test results indicated that concrete beams reinforced with CFRPRS stirrups could maintain shear behavior comparable to that of the concrete beam reinforced with steel stirrups. Compared with the beams with conventional CFRP stirrups with circular sections, superior shear behavior was observed for the beams reinforced with CFRPRS stirrups in terms of shear strength and crack width. [ABSTRACT FROM AUTHOR]

Concrete beams reinforced with a combination of steel and fiber-reinforced polymer (FRP) bars can provide increased strength, serviceability, and durability. However, the amounts of FRP and steel necessary to ensure sufficient strength and ductility are unclear. Because of the linear elastic behavior of FRP bars before failure, the deformation characteristics of hybrid reinforced concrete beams differ from those of conventional steel reinforced concrete beams and pure FRP reinforced concrete beams. Conventional ductility indices are not suitable for concrete beams in hybrid reinforcement approaches. To ensure the ductile failure of beams, proper reinforcement ratio limits are proposed. In addition, a new ductility index is defined in terms of deformability and energy absorption capacity. Various comparisons between experimental results and theoretical predictions show that the developed models can accurately predict the load capacity and ductility. In addition, the influences of various parameters on ductility are discussed. Based on various requirements for ductility, reasonable ratios of FRP to steel bars are found. [ABSTRACT FROM AUTHOR]

This paper describes the procedure recommended in two specific standards to define and quantify structural redundancy using a direct analysis of bridges. The procedure is illustrated using two typical bridge configurations. The first example is a simply-supported truss bridge superstructure. The second example is a continuous three-span two-girder steel box bridge. These examples are selected because these types of structures are generally considered to be fracture-critical nonredundant bridges. The object of analysis is to investigate the reserve strength redundancy of the structures, defined as their ability to continue to carry loads after the limiting strength of one member is reached. The analysis also investigates the loads that the structures could still carry after brittle damage to one of their members. The results of the analysis show that both structure types can provide adequate levels of redundancy for overloading, assuming that the bridge members have been designed to satisfy the applicable specifications. Also, the analysis demonstrates that neither bridge is necessarily fracture-critical in the traditional sense because the failure in any of their steel tension members is not expected to result in a partial or full collapse of the bridge. However, the truss bridge may be labeled as "damage-critical" because the failure of a compression chord would significantly reduce the bridge's ability to carry vehicular traffic in a damaged state. [ABSTRACT FROM AUTHOR]

The study presented in this paper is arguably the first study to use a self-organizing map (SOM) for global structural damage detection. A novel unsupervised vibration-based damage detection algorithm is introduced using SOMs in order to quantify structural damage. In this algorithm, SOMs are used to extract a number of damage indices from the random acceleration response of the monitored structure in the time domain. The summation of the indices is used as an indicator which reflects the overall condition of the structure. The ability of the algorithm to quantify the overall structural damage is demonstrated using experimental data of Phase II experimental benchmark problem of structural health monitoring. [ABSTRACT FROM AUTHOR]

Segregation of grout applied for the protection of posttensioning steel may cause corrosion of steel wires, leading to serious hazards to the safety of posttensioned structures. Several cases of failure of external tendons of bridges have been documented arising from heavily corrosion attacks initiated and propagated in the presence of an unhardened (soft) whitish paste generated by segregation. The reasons for this aggressive corrosion attack are not clear, and improving the knowledge on the properties of the segregated grout would help in clarifying this phenomenon. Chemical, physical, and microstructural properties of grouts collected from the ducts of a bridge where segregation occurred are investigated. Results describe the different stages of segregation of the grout and show that the aggressiveness of the whitish grout could be associated with the high content of soluble compounds produced by early hydration of cement, especially alkalis, which lead to pH values exceeding 14. [ABSTRACT FROM AUTHOR]

This study describes a self-tensioning system in which the gravitational loads acting on a horizontal structural element are automatically converted to a posttensioning force on that component. The self-tensioning effect has a variable intensity, constantly adjusted depending on the applied service loads. The self-tensioning is eccentrically applied over the cross section, and it generates a negative moment that compensates the deformations due to the gravitational loads. The system can be utilized in beams, slabs, and structural framings of different materials and can be implemented using different mechanical and hydraulic solutions. The study describes the operation of a mechanical solution for the self-tensioning system and analyzes its behavior in large-span timber floor framings. When combined with conventional pretensioning, the self-tensioning system notably improves the strength and deformation behavior and permits a design of timber floor framings with a total height of 0.03 times the span length, achieving relative deflections below 1/1,000 of the span for the service loads of the structure. [ABSTRACT FROM AUTHOR]

Development of a simplified approach for monitoring the cables of cable-stayed bridges is described in this article. The method introduced in this paper uses the distributed measurement of strains along the bridge deck to detect the cables that have totally or partially lost their tensile force. The fundamental principle employed in formulating the method is the interrelationship between the individual cable forces and the bending moment along the bridge span. The proposed method was evaluated through an experimental program that involved fabrication and testing of a reduced scale model of a single plane cable-stayed bridge. Distributed strain along the span length was monitored by a Brillouin Optical (Neubrex, Hyogo, Japan) Time Domain Analysis fiber optic sensor system. Strain gauges, Fiber Bragg Grating sensors (Technica Optical Component, LLC, Beijing, China), and a finite element model of the bridge were employed for evaluating the efficiency of the proposed method. Several different damage cases were considered in the experiments, including single and multiple cable tension loss scenarios. Experimental results revealed that it was possible to detect the cables that had experienced tension losses of 30% or more. [ABSTRACT FROM AUTHOR]

The shear behavior of fiber-reinforced-polymer-strengthened reinforced concrete (FRP-strengthened RC) members is not fully developed and accurately predicted because of the lack of accurate constitutive laws for the components of the composite members. This paper presents experimental and analytical investigations of tensile stress-strain relationships of concrete and steel in FRP-strengthened RC members. These stress-strain relationships are required in formulations of softened truss models to predict the shear behavior of the FRP-strengthened RC element. Thirteen full-scale FRP-strengthened RC prismatic specimens with different FRP reinforcement ratios, steel reinforcement ratios, and FRP wrapping schemes were tested under uniaxial tension loading. The results show that the tensile behavior of the concrete and steel is altered because of the externally bonded FRP sheets. Modified constitutive laws are proposed and incorporated in the softened membrane model (SMM) to demonstrate through two tests the behavior of FRP-strengthened RC element subjected to pure shear. Moreover, crack spacing and crack width were studied and compared with existing code provisions. [ABSTRACT FROM AUTHOR]

In the present study, a new method is introduced for confining square concrete columns in which fiber-reinforced polymer (FRP) strips are used at corners and FRP battens on column sides. In this method, FRP battens confining the section do not undergo any curvature but similar to what happens in flat coupons, they are stretched as completely flat strips. To compare the proposed method with the intermittent wrap technique, 25 square reinforced-concrete (RC) columns with cross-sections of 133 × 133 mm and heights of 500 mm were subjected to load eccentricities of 0, 30, 60, 90, and 120 mm. The test parameters included the technique employed for confining columns, flexural strengthening technique, and applied load eccentricity. The experimental results demonstrated that confining battens in the new method of corner strip-batten are uniformly stretched under the tension stresses of confinement; therefore, more-uniform distribution of confining pressure on section occurs and stress concentration at corners is eliminated. Thus, compared to both unconfined and intermittently-wrapped RC columns, square RC columns confined through the corner strip-batten technique exhibit improved performance in terms of enhanced load-carrying capacity and ductility under eccentric loading. Finally, axial loading–bending moment (P–M) interaction diagrams were drawn for the strengthened columns. Comparison of the experimental results with those obtained from the expressions suggested in different codes revealed that the estimates of the codes were conservative when compared to experimental measurements. [ABSTRACT FROM AUTHOR]

This study reports the findings of an experimental investigation into the behavior of an inclined shear plane in reinforced concrete, such as a diagonal crack in the web of a beam, strengthened with externally bonded carbon fiber–reinforced polymer (CFRP) fabric. A modified push-off test of novel geometry was developed for this study. This test generates a diagonal failure plane subject to combined shear and tension. Both unwrapped and wrapped tests were conducted, allowing the load sharing and load-displacement behavior of the reinforced concrete, and the reinforced concrete with externally bonded CFRP fabric, to be investigated. Fully wrapped and U-wrapped CFRP fabric configurations were tested. Results indicate that for the arrangement tested, concrete, steel, and CFRP contributions to resistance are not independent, and that effective anchorage lengths given in the United Kingdom and United States guidance for U-wrapped CFRP may not be adequate in some cases. [ABSTRACT FROM AUTHOR]

This paper discusses contemporary design procedures for fillet welds to hollow structural sections (HSS) in several prominent design codes. The structural reliability associated with the directional strength-enhancement factor contained in North American Specifications is examined, based on a set of laboratory tests on fillet-welded connections between HSS and rigid end-plates. A total of 33 connections, in which the welds had been designed to be the critical elements, were tested to failure by axial tension loading applied to the HSS members. The experimentally obtained weld strengths were compared to the predicted nominal strengths. The directional strength-enhancement factor was found to lead to unsafe strength predictions, particularly for large weld sizes. Hence, a restriction on the use of this factor for fillet welds to HSS members, in North American steel design specifications, needs to be considered. The analysis also shows that Eurocode 3 fillet weld design provisions give conservative strength predictions. [ABSTRACT FROM AUTHOR]

Posttensioning low-damage technologies were first developed in the late 1990s as the main outcome of the U.S. Precast Seismic Structural System (PRESSS) program coordinated by the University of California, San Diego, and culminated with the pseudo-dynamic test of a large-scale five-story test building. The extension of posttensioned techniques to timber elements led to the development of new structural systems, referred to as Pres-Lam (prestressed laminated timber). Pres-Lam systems consist of timber structural frames or walls made of laminated veneer lumber, glue laminated timber (Glulam), or cross-laminated timber (CLT). Pres-Lam walls consist of a rocking timber element with unbonded posttensioned tendons running through the length and attached to the foundation, which provides a centering force to the wall, while energy dissipation is supplied by either internal or external mild steel dissipaters. Previous tests carried out on posttensioned timber walls focused on small-scale (one-third) specimens with the main objective of evaluating the general response of the system. The main objective of the experimental program herein presented is the testing and estimating of the response of a series two-thirds-scale posttensioned walls, with alternative arrangements and combination of dissipaters and posttensioning, focusing on the construction details adopted in real practice. The paper first presents a brief discussion on the seismic demand evaluation based on the displacement-based design approach. The construction detailing of the steel dissipater connections, posttensioning anchorage, and shear keys are then presented. The main objectives of this experimental program were the investigation of the experimental behavior of large-scale posttensioned timber walls, with particular focus on the system connection detailing and optimization of posttensioning anchorage, fastening of the dissipation devices, and shear keys. The program consisted of several quasi-static cyclic tests considering different steel dissipater configurations, different levels of posttensioning initial stress, and different dissipater options were considered: both internal and external mild steel tension-compression yield devices were used. The experimental results showed the performance of posttensioned timber wall systems, which provide a high level of dissipation while showing negligible residual displacements and negligible damage to the wall element. The final part of the paper presents the experimental evaluation of the area-based hysteretic damping for the tested specimens, and the results highlight the great influence of the connection detailing of the dissipaters. [ABSTRACT FROM AUTHOR]

Uncertainties can be introduced into the structural performance of cable-network antennas by inevitable manufacturing errors, which may result in failure in service. In this paper, robust optimization is first adopted to address the design of cable-network antenna structures with imperfect cable lengths. First, an analytical sensitivity analysis method is proposed to evaluate the effects of the uncertainties on the shape precision and cable tensions. Second, based on the sensitivities, the mathematical model of the robust design is established. At last, the proposed method is applied to a 3-m-diameter cable-network antenna structure. The analytical sensitivities are validated by comparing with the sensitivities computed by finite-difference method, and the feasibility of the presented robust design model is demonstrated by Monte Carlo simulations. The numerical experiments show that the robustness is greatly increased by the application of the robust design method. The results recommend that higher tension level, more elastic cables, thicker tension ties, and slenderer net cables can benefit the robust ability of cable network antenna structures. [ABSTRACT FROM AUTHOR]

A half-scale three-bay by three-bay steel-concrete composite floor system, which represented gravity framing for a typical commercial building, was studied experimentally to evaluate its structural integrity under four separate column removal scenarios: a corner column, two edge columns, and an interior column. In each test, the load was incrementally applied in the bays that were tributary to the removed column using water in containers that were placed on top of the slab. The tests demonstrated that gravity systems for commercial buildings have a significant level of structural integrity--compared to the load redistribution capability expected for steel framing with simple shear connections--even without specific design against progressive collapse. In the corner and edge column removal scenarios, 2.9 kPa (60 psf) and 4.0 kPa (83 psf) were sustained, respectively, and these loads represent a range of 50-75% of the expected floor load. The interior column removal scenario had an unexpectedly low capacity of 3.2 kPa (67 psf), but the behavior was heavily affected by damage to the test specimen due to the previous edge column removal scenarios. For this interior column removal scenario, the lack of slab continuity at the interior edges of the loaded bays prevented composite action and load redistribution occurred primarily through tension ties. Although tension tie development was observed in this experimental program, composite flexural response also had an important contribution to load redistribution for the corner and edge column removal scenarios. Despite the load redistribution seen in these tests, the observed capacities are below the extreme event load combination that is commonly used when designing to prevent progressive collapse, so the current design practice for steel gravity framing is likely not sufficient to meet this criterion. [ABSTRACT FROM AUTHOR]