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Scouring of pile group foundations is a common phenomenon for cross-river bridges and can produce significant damage in earthquake-prone regions. This study experimentally investigated the seismic failure mechanism and postearthquake vertical load-carrying capacity of scoured pile group foundations. Three identical 2 × 3 reinforced concrete (RC) pile group specimens were embedded in homogeneous medium density sand with an overall scour depth equal to five times the diameter of a single pile, and then were subjected to lateral cyclic loads applied to the pile cap in order to produce a predetermined damage state in the piles. Pushover in the vertical-downward direction (pushdown) was finally applied on these damaged specimens exhibiting a permanent lateral displacement to evaluate their residual load-carrying capacities. Experimental results show that the leading pile was more prone to seismic damage, as both the first aboveground and first belowground plastic hinges originally occurred on it. The embedded depth of potential plastic hinges in leading, middle, and trailing piles gradually increased. In addition, the extension of pile damage had a significant influence on the residual vertical load-carrying capacity and the corresponding vertical failure mode of the pile group. Reductions of 10.4%, 47.5%, and 73.8% in the vertical load-carrying capacity of these scoured pile group specimens were recorded when they previously suffered a displacement ductility of 1.75, 3.5, and 5.0, respectively. Based on the experimental results, a linear degradation formula on the normalized postearthquake vertical load-carrying capacity of pile groups with respect to the displacement ductility was developed. The experimental results presented in this paper could be used to validate the ductility capacity and residual vertical load-carrying capacity of pile groups numerically evaluated by using three-dimensional nonlinear finite-element models. This research represents also a first step toward the development of a rapid postearthquake assessment approach for bridges with pile group foundations.

This paper introduces an updated formulation of a five-step procedure dealing with the design of fluid viscous dampers for the seismic retrofitting of existing frame buildings. The original design procedure is known as the "direct five-step procedure," and is articulated into 5 consecutive steps guiding the designer from the identification of the expected seismic performances, to the sizing of the added viscous dampers up to the final verification of the seismic behavior through nonlinear dynamic time history analyses. The procedure leads to the full definition of the mechanical characteristics of the commercial non-linear viscous dampers and allows to estimate the maximum dissipative forces acting in the dampers and the internal forces in the frame members. The objective of the design procedure, when applied to a new building, is to size the dampers in order to keep the structural elements within the linear elastic range considering a "rare" earthquake design level. However, when dealing with an existing building, especially if originally designed considering vertical loads only, the insertion of viscous dampers could be not sufficient to keep the structural elements in the elastic range. Thus, it might be necessary to accept local plastic excursion of the structural elements, by taking into account the ductility capacity (albeit probably limited) of the structural members (hysteretic dissipation associated with damage in beams and columns). This latter aspect is explicitly considered in the updated formulation of the "direct five-step procedure" presented here through the introduction of an overall response reduction factor accounting for both the ductility capacity of the structural members and the viscous damping provided by the added dampers. The design procedure is then applied to a 11- storey frame structure case study, which is representative of reinforced concrete buildings designed for vertical loads only. Three different retrofitting design strategies are considered, based on different exploitation of viscous energy dissipation provided by the dampers and hysteretic energy dissipation due to the excursion of the structural members into the inelastic regime. [ABSTRACT FROM AUTHOR]

This paper introduces an updated formulation of a five-step procedure dealing with the design of fluid viscous dampers for the seismic retrofitting of existing frame buildings. The original design procedure is known as the “direct five-step procedure,” and is articulated into 5 consecutive steps guiding the designer from the identification of the expected seismic performances, to the sizing of the added viscous dampers up to the final verification of the seismic behavior through non-linear dynamic time history analyses. The procedure leads to the full definition of the mechanical characteristics of the commercial non-linear viscous dampers and allows to estimate the maximum dissipative forces acting in the dampers and the internal forces in the frame members. The objective of the design procedure, when applied to a new building, is to size the dampers in order to keep the structural elements within the linear elastic range considering a “rare” earthquake design level. However, when dealing with an existing building, especially if originally designed considering vertical loads only, the insertion of viscous dampers could be not sufficient to keep the structural elements in the elastic range. Thus, it might be necessary to accept local plastic excursion of the structural elements, by taking into account the ductility capacity (albeit probably limited) of the structural members (hysteretic dissipation associated with damage in beams and columns). This latter aspect is explicitly considered in the updated formulation of the “direct five-step procedure” presented here through the introduction of an overall response reduction factor accounting for both the ductility capacity of the structural members and the viscous damping provided by the added dampers. The design procedure is then applied to a 11-storey frame structure case study, which is representative of reinforced concrete buildings designed for vertical loads only. Three different retrofitting design strategies are considered, based on different exploitation of viscous energy dissipation provided by the dampers and hysteretic energy dissipation due to the excursion of the structural members into the inelastic regime.

Scoured pile-group foundations (SPGFs) are susceptible to inelastic deformation during earthquakes. Hence, the ductile behavior of SPGFs has become a rising concern in academic and industrial communities. Traditionally, pushover analyses with single-point load patterns have been adopted to obtain the ductile characteristics of bridge pile-group foundations. However, this practice cannot properly account for the inertial effects from both the superstructure and the pile-cap. Accordingly, in this study, the well-known incremental dynamic analysis (IDA) was adopted to rigorously and comprehensively investigate the ductile behavior of SPGFs for the seismic design of bridges in flood-prone regions. To this end, a shake-table test on an SPGF-supported RC bridge bent model was firstly employed to validate the adopted numerical modeling technique. An in-depth parametric study was then conducted on the bridge bent with the damage potential of the SPGF embedded in cohesionless soil, considering various structural and geotechnical parameters. Based on the IDA results, the seismic failure process, structural limit states, and ductile performance indices of SPGFs were systematically investigated. It was found that the failure process of SPGFs obtained from IDA was consistent with that reported in a previous quasistatic test. Scoured pile-group foundations have a considerable displacement ductility capacity (quantified as 2.48 and 3.47, on average, for the easy-to-repair and ultimate states, respectively), as well as lateral strength enhancement capacity (i.e., the lateral strength values for the easy-to-repair and ultimate states were, on average, 1.40 and 1.46 times that of the first-yield state, respectively). The displacement ductility capacity of SPGFs can be improved by using more rows of piles, a larger pile diameter, a higher transverse confinement of the pile section, a lower longitudinal reinforcement ratio of the pile section, or a larger pile spacing. Those with a shorter aboveground pile height (scour depth), or supporting a shorter pier, exhibited a larger displacement ductility capacity. [ABSTRACT FROM AUTHOR]

Scour can increase the earthquake-induced damage in pile group foundations. Quantifying the parameter sensitivity of the seismic performance for scoured pile group foundations is essential for the optimal design and retrofit of bridges located in seismic-prone regions. Such quantification requires numerical models that are computationally efficient and accurate in describing the mechanical behavior associated with the complex soil–foundation–structure interaction of these systems. This study proposes an efficient finite-element model (FEM) of pile groups based on a beam on the nonlinear Winkler foundation approach. This FEM uses asymmetric p-multipliers to describe the different soil resistance exerted on leading and trailing piles when applying cyclic lateral loads. The proposed FEM is validated by comparing the numerical response with the experimental measurements taken from a quasi-static test available in the literature and is used to perform an extensive parametric sensitivity analysis to quantify the response sensitivity to 11 structural and soil parameters. Tornado diagrams are employed to identify an importance ranking of these parameters on the seismic performance of scoured pile groups. The obtained results indicate that the proposed FEM is able to capture both the global and local structural responses of pile group foundations. The parametric sensitivity analysis shows that pile group foundations have considerable ductility capacity. Pile diameter and axial load ratio of piles are the most important parameters for the seismic performance of pile groups. Increasing the pile diameter is the most efficient approach to improve the seismic performance of a pile group when considering scour effects. The seismic performance of a scoured pile group deteriorates with increasing piles' axial load ratio. For a deep pile group foundation, seismic performance is very little sensitive to pile length and relative density of sand. Based on the results of the parametric analysis, recommendations are proposed for the seismic design of pile group foundations with scour effects. [ABSTRACT FROM AUTHOR]

The current research on the damage-based strength reduction factor has been completely based on the inelastic single-degree-of-freedom systems that are more suitable for two-dimensional analyses. Therefore, it is necessary to construct damage-based strength reduction factor spectra for systems subjected to bidirectional ground motions. In this study, an inelastic single-mass bi-degree-of-freedom (SMBDOF) system subjected to the orthogonal bidirectional ground motions with the hysteretic property of two-dimensional yield-surface plasticity function is presented, and the x -component of the system is used to construct the damage-based strength reduction factor spectra of the system (R b spectra). The Park-Ang damage model is used to determine the constant damage index of the R b spectra. In addition, 178 ground motion records for site classes C, D, and E are considered as ground excitations of the SMBDOF system to construct the mean R b spectra with the format of R b - D - T for a given ductility capacity and R b - μ u - T for a given damage level. The R b spectra of the SMBDOF system is compared with the corresponding R spectra of the SDOF system. Statistical analysis considering different values of the natural period, ductility capacity, damage index, period ratio, and site condition is conducted. Analysis results show that the coupling of two-component responses of an inelastic system could increase the strength demand of the system in certain cases; the trend of the R b spectra presented in this study is approximately consistent for different site classes, but the spectral values have the characteristic of site conditions. Therefore, the influence of the period ratio should be considered because a large period difference between two components of the SMBDOF system could aggravate seismic damage in certain situations. Based on the statistical analysis, the expression of R b spectra curves with a period ratio γ = 1 is derived using the regression analysis, and the correction expression is obtained considering the influence of the period ratio on the R b spectra. Then, the construction procedure of the R b spectra is introduced. The predicted R b spectra obtained by the proposed procedure is compared with the actual mean spectra, and comparison results indicate a good match. [ABSTRACT FROM AUTHOR]

This paper investigated the effect of concrete strength on the seismic performance of circular reinforced concrete (RC) columns confined by basalt and carbon fiber-reinforced polymer (BFRP and CFRP). Eight confined columns and four control columns were tested under a low cyclic lateral load. The variables in the test included concrete compressive strength (i.e., 22.4 MPa, 31.4 MPa, 42.5 MPa and 57.8 MPa) and FRP type (i.e., basalt and carbon fiber). The test results demonstrated that all the columns exhibited flexural failure after confinement. The strength, ductility and energy dissipation capacity of the confined columns were effectively enhanced. With the same confining stress, the peak loads of the BFRP- and CFRP-confined columns were nearly the same. However, the BFRP-confined columns with low and moderate concrete strength showed larger ductility and energy dissipation capacity compared with the CFRP-confined counterparts, and these capacities of the CFRP-confined column with a concrete strength of 57.8 MPa were slightly better than those of the BFRP-confined equivalent. This showed that the FRP jackets with larger modulus had better confinement effect on the columns with higher concrete strength. Finally, formulas for calculating the load carrying and ductility capacities of different FRP-confined circular RC columns were proposed based on the experimental results. • Experiments explored the seismic performance of twelve circular RC columns with parameters of concrete strength and FRP type. • Load capacities, ductility and energy dissipation of confined columns with different FRP and concrete strength were compared. • Theoretical models of load carrying and ductility capacities for different FRP-confined columns were developed based on test results. [ABSTRACT FROM AUTHOR]

The present paper continues a series of the authors’ studies on improving conventional concentrically braced frames (CBFs). In previous works, the authors equipped a CBF with a restrained local fuse to improve its behavior, thus introducing local fuse–auxiliary element concentric braces (LF-AECBs). The mechanism of LF-AECBs with a restricted fuse in the length increased the ductility and energy dissipation capacity of the bracing system by limiting the overall buckling locally to the compressive zone. However, further numerical studies suggested that due to early buckling, now local, the restrained local fuse could not be exploited until the failure. Therefore, this study introduces an improved local fuse–auxiliary element concentric brace (ILF-AECB) to fix the issue. Numerical studies are also done to determine the optimal shape of ILF-AECBs in order to obtain maximum energy dissipation capacity and ductility under cyclic loading. In this article, the results of experimental and numerical studies show that ILF-AECBs with a new formulation delaying the fuse buckling completely succeed in using the full capacity of the local fuse for energy dissipation and ductility. Moreover, the analytical study shows that the frame equipped with ILF-AECB offered much better performance in terms of energy dissipation and reduction of the input demand to the structural elements compared to the similar CBFs.

This paper investigates the seismic behavior of the rectangular-reinforced concrete columns subjected to pure flexure, pure torsion, and combined flexural-torsional loadings using 4 quarter-scaled experimental specimens. During flexural-torsional loading, the axial rotation to the relative displacement ratios were considered to be 2 and 4. The ultimate displacement capacity and the flexural moment capacities of the specimens under combined flexural-torsional loadings were found to be decreased compared to the pure-flexural case for different rotation over drift ratios. An equation expressing the interaction curve between the flexural and torsional moment strength capacity of rectangular-reinforced concrete sections is proposed. [ABSTRACT FROM AUTHOR]

This paper investigates the cyclic behavior of steel columns subjected to single‐sided cyclic loading protocols driven by residual deformations. First, nonlinear time‐history analyses are performed to steel framed structures using a set of repeated earthquakes. Then, based on the dynamic analysis results, a set of single‐sided loading protocols is developed to envelop the asymmetric seismic behavior of the examined frames. The developed protocols are used to identify the new single‐sided capacity margins of steel columns in terms of strength and ductility as well as evaluate the potential of using novel high‐strength materials. In this paper: (a) the new asymmetric loading protocols are proposed based on the seismic behavior of three medium‐rise frame buildings with different beam‐to‐column strength ratios (i.e. Mpc/Mpb) which are analyzed with the aid of the finite element analysis (FEA) software ABAQUS; (b) a computational databank of the inelastic responses of square tubular steel columns with high yield‐to‐tensile (YT) strength ratio is developed by subjecting column FEA models with various width‐to‐thickness ratio and axial loads to both conventional and asymmetric cyclic loading protocols. Due to the asymmetrical nature of the cyclic protocols, a lower post‐peak strength deterioration was observed in columns that enables the definition of new, extended, ductility capacity margins. The ductility capacity ratios under the asymmetric loading protocols were found to be 1.15 to 1.71 higher than those obtained under the conventional protocols enabling the use of high‐strength steels in steel columns of smaller width‐to‐thickness ratio. [ABSTRACT FROM AUTHOR]

This study aims to consider the effect of soil–structure interaction (SSI) on the ductility and hysteretic energy demands of superstructures and propose empirical equations for demand prediction in soil–structure systems. To this end, the FEMA 440 procedure was considered to develop nonlinear single-degree-of-freedom oscillators with a period range of 0.1–3.0 s, as the representative of superstructures. The elastic-perfectly plastic and a moderate pinching degrading hysteretic models were considered for the nonlinear response of the superstructure. The model of the nonlinear soil–foundation system was developed through the Winkler method. In this regard, the type of soil beneath the foundation was assumed as D category, according to the site classification in ASCE 7-10. A wide range of key parameters, including the strength reduction factors (2 ≤ Rμ ≤ 8), the foundation safety factor (3 ≤ SF ≤ 7), the foundation-to-structure height aspect ratio (1 ≤ h/b ≤ 5), and the foundation length-to-width ratio (3 ≤ Lf/Bf ≤ 20) was introduced into the analytical models to conduct parametric studies. Results show the considerable effect of SSI on reducing the ductility and hysteretic energy demands in superstructures with short fundamental periods. More demand reduction can be achieved by providing the lateral sliding of the foundation on the soil surface, especially for systems with a small aspect ratio. The pinching–degrading hysteretic behavior of the superstructure remarkably modifies the level of demands. Moreover, predictive models were proposed for estimating the ductility and hysteretic energy demands in flexible base systems. These models modify demands in the rigid base structures based on their physical and mechanical properties. The developed models consider the effects of structural hysteretic behavior as well as foundation flexibility. The efficiency of the proposed model was assessed on a multi-story frame. Finally, the required ductility capacity of the systems was determined through the Park–Ang damage index and by using the developed predictive models. Results show the efficiency of the empirical models to reasonably estimate the required ductility capacity. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the length of the gusset-plate hinge zone proposed by Iranian National Building Code (Part 10) for Special concentrically braced frames (SCBF). For this purpose, numerical studies were done on the seismic behavior of this frames using ABAQUS software. Numerical modelling procedure is validated using the reproduction of the results of an experimental study. A five story building with Special diagonal concentrically braced frames was modeled in ETABS software and a portal frame from the first story of the building was considered for investigation. The detailing of the frame was designed for tension and compression based on Iranian code. Seismic behavior of single and double tapered gusset plates with various connection angles and dimensions as well as various length of the hinge zones including -3t, -2t, -t, 0t, t, 2t and 3t were investigated using nonlinear cyclic deformation loading to the ATC-24 test protocol.Seismic behavior of the connections were studied based on ductility, number of cycles before failure, drift before failure and tension and compression strength.Evaluation of the failure limit of the models was carried out using the concept of equivalent plastic strain. Based on the results of the investigated models it can be said that: It is not recommended to use double gusset plates instead of single ones for SCBFs. Gusset plates with a 15 degree angle of inclination have higher ductility capacity and better seismic behavior than ones with a 25 degree angle of inclination. For single gusset plates with a 15 degree angle of inclination, the appropriate length of the hinge zone is -2t, which is not consistent with Iranian code. For single gusset plates with a 25 degree angle of inclination, the appropriate length of the hinge zone is 2t, which is consistent with the Iranian code.

The X-bracing system is one of the lateral loads bearing system. In X-bracing system’s elements, axial plastic hinges (compressive or tensile) will be formed instead of flexural hinges which are not capable to absorb high energy. Seismic performance can be improved by replacing these plastic hinges with the bending plastic joints. In this study, a new kind of X-bracing named X-bracing equipped with flexural yielding damper is introduced in which the plastic axial hinges is substituted by flexural plastic hinges. In this kind of bracing the failure mechanisms focuses on flexural hinges. The objective of this study is to evaluate the seismic performance of this kind of bracing. For this purpose, several X-bracing frames with various stories was selected and designed based on Iranian building codes. The seismic performance of these frames (stiffness capacity, strength capacity, and ductility capacity) and force reduction factors were evaluated using static and time history nonlinear analysis. In dynamic time history analysis seven acceleration-time records was applied. The results show that the damper reduces stiffness and strength capacity inconsiderably, but increases the ductility capacity significantly. It also increases the force reduction factor of the frames significantly. The amount of force reduction factor for this system is the same as eccentrically braced frame one.

• Quantifying the fracture-leading ductility through tested square HSS braces. • Developing ductility-based fragility curves to estimate fracture of HSS braces. • Seismic risk assessment of braced frames in existing buildings. • Fracture probability of fracture of HSS braces is high at expected demand levels. A study on the seismic ductility demands on square HSS braces in special concentrically braced frames (SCBFs) is presented to address the seismic risk of braces in existing SCBF buildings designed according to both previous and current AISC Seismic Provisions. First, the paper discusses the development of ductility-based fragility curves by employing specimens with various width-to-thickness and slenderness ratios collected from 16 experimental programs from 1978 to today. Second, the constructed fragility curves are used to estimate the vulnerability of square HSS braces to the damage state of fracture using the brace ductility demand as engineering demand parameter. Then, the seismic risk of braces in terms of fatigue life is evaluated under 30 earthquake ground motions using a seven-story office building designed following requirements of previous and current design practice. The study concludes that braces in SCBF designed in compliance with the previous and current AISC Seismic Provisions are subject to a high probability of fracture under earthquake ground motions characterized by different intensity levels, which in turn might lead to underestimation of the overall seismic risk. [ABSTRACT FROM AUTHOR]

Abstract In many engineering applications the limit analysis theorems can be used to estimate the ultimate capacity of several structures. However, the limit analysis can be applied on structures with an adequate plastic capacity. When the goal is to evaluate the ultimate capacity of masonry structures, they could show some drawbacks. For this reason, the incremental analysis represents a valid alternative to estimate the ultimate capacity of masonry structures. These structures could show brittle failures before the hinge mechanism. It is a key aspect especially for curved masonry elements like as arches and vaults. The work focuses on the incremental analysis of masonry barrel vaults without backfill. An analytical model in the framework of the incremental analysis has been proposed. The analytical model allows to assess both the ultimate capacity and the ductility of the masonry barrel vaults. In the first part, the proposed model has been discussed. Then, parametric analysis was performed to assess the impact of physical, geometrical and mechanical parameters on the ultimate behaviour. The numerical results allow to identify some structural examples where the brittle behaviour becomes crucial. Finally, the proposed model was validated with experimental results on a full-scale masonry barrel vault. Highlights • The work focuses on the incremental analysis of masonry barrel vaults without backfill, accounting for tensile strength. • The analytical model allows to assess both the ultimate capacity and the ductility of the structure incrementally. • The numerical results allow to identify some structural examples where the brittle behaviour becomes crucial. • The proposed model was validated by using the experimental tests of a masonry barrel vault actually tested. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of a multi-span steel frame retrofitted with a minimal disturbance arm damper (MDAD). The primary objective of the paper is to analyze and verify the retrofit mechanism in terms of force redistribution. An elastic design of the MDAD, targeting the reduction of the positive bending moment at beam ends was first developed for the seismic rehabilitation of steel frames having a beam-collapse mechanism. Here, the composite beams under positive bending sustain tensile force at the bottom flanges. Its effectiveness was examined experimentally and numerically. This study also explored the effect of the MDAD on delaying the fracture of the beam ends. Particularly, the behavior of the retrofitted steel frame after the fracture of beam ends was majorly focused. By comparing the test results of specimens with and without MDAD, it was found that the MDAD successfully reduced the positive bending moment of the beam ends as intended in the proposed design equation and delayed the fracture. The retrofitted substructure did not exhibit strength deterioration even after beam end fracture because of the backup load resistance provided by the MDAD. Finally, enhancement of the collapse limit by the MDAD is discussed through numerical simulations for a moment-resisting steel frame. [ABSTRACT FROM AUTHOR]

The ductility capacity of bridge piers is estimated uniaxially by moment-curvature analysis, regardless of the amount of flexural demand on the perpendicular axis of the section. In this study, by applying a numerical fiber-based model, the ductility capacity of reinforced concrete (RC) piers subjected to biaxial monotonic loadings is investigated. 288 RC cantilever columns with 6 different square/rectangular solid/hollow sections are studied. Variations in shape, aspect ratio, dimensions, axial compression force, concrete characteristic strength and longitudinal reinforcement ratio are considered in the defined samples. Monotonic biaxial displacement demand is applied at the top of the cantilever columns. Different monotonic displacement paths are defined by varying the angle between the loading alignment and the major axes of the section. In order to sum up and interpret the responses obtained from different samples, a framework is developed to derive normalized ductility capacity ratios ( R Δ ). Based on the findings in this study, the maximum reduction of the mean ductility capacity ratio ( R Δ ‾ ) is about 15% and 8% for solid and hollow rectangular RC sections, respectively. According to the obtained results, the maximum reduction of ductility capacity of square and rectangular sections occurs when ϕ angle is between 40°–50° and 50°–70°, respectively. Based on the obtained mean ductility capacity ratios ( R Δ ‾ ), a bi-linear equation is proposed for evaluating the ductility capacity of rectangular RC sections under biaxial flexural demands. [ABSTRACT FROM AUTHOR]

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This paper presented an experimental study on the failure mode, ultimate bearing capacity and ductility capacity of PVC-CFRP confined reinforced concrete columns subject to low cyclic loading. Several parameters, such as the axial compression ratio, shear span ratio, and hoop spacing of CFRP strips were considered in the analysis. The results showed that all columns at low axial compression ratio failed by bending. The long and short columns with large hoop spacing at high axial compression ratio failed by flexural shear while the short columns with small hoop spacing at high axial compression ratio failed by shear. The ultimate bearing capacity increased as the axial compression ratio increased or the shear span ratio decreased while the ultimate bearing capacity decreased as the hoop spacing of CFRP strips increased. The ultimate strains located at the bottom of the column increased as the axial compression ratio increased while the ultimate strains decreased as the shear span ratio increased. The confining effect of CFRP strips increased gradually as the hoop spacing of CFRP strips decreased. The ductility capacity decreases as the axial compression ratio or the shear span ratio increased while the ductility capacity increases as the hoop spacing of CFRP strips increased. [ABSTRACT FROM AUTHOR]

Crescent Shaped Braces, CSBs, are steel hysteretic devices which, thanks to their geometrical configuration, are characterized by an enhanced seismic behavior that makes them a promising alternative to conventional diagonal steel braces and other seismic devices such as Buckling Resisting Braces and Scorpions. The present work reports the results of the first experimental campaign devoted to assess the cyclic experimental behavior of CSBs. The main goals of the experimental campaign are: (i) to verify/compare the effectiveness of design formulas for the seismic design of CSB introduced by the authors in a previous research work and the predictions of a simplified non-linear model in terms of force-displacement envelop response; (ii) to assess the experimental non-linear cyclic behavior in terms of ductility capacity, energy dissipation capacity, failures. [ABSTRACT FROM AUTHOR]

A simple relationship is proposed in this paper to construct damage-based inelastic response spectra including the effect of ground motion duration that it can be used for damage control in seismic design of structures. This relation is established for three groups of ground motions with short-duration, moderate-duration, and long-duration ranges. To develop the model, the duration effect is included in the cyclic ductility of structures by an energy-based method, and then strength reduction factors are computed based on this modified ductility (named [ABSTRACT FROM AUTHOR]

The seismic responses of steel buildings with perimeter moment resisting frames (MRF) with welded connections (WC) are estimated and compared to those of similar buildings with semi-rigid post-tensioned connections (PC). The responses are estimated in terms of ductility reduction factors (R , ), ductility demands ( µ ) and force reduction factors ( R). Two steel model buildings, which were modeled as complex-3D-MDOF systems, were used in the study. Results indicate that the reduction magnitude of global response parameters is larger than that of local response parameters, contradicting the same reduction implicitly assumed in the static equivalent lateral force procedure, implying that non-conservative design may result. The value of 8 for R, suggested in many codes for ductile steel MRF, and the value of 1 suggested in the well known Newmark and Hall procedure for the ratio of R to µ , cannot be justified. The reason for this is that SDOF systems were used to model actual structures, where higher mode effects, energy dissipation and structural overstrength weren't explicitly considered. The codes should be more transparent regarding the magnitude and the components involved in the force reduction factors. The seismic performance of steel buildings with PC may be superior to that of the buildings with WC, since their force reduction factors are larger and their ductility demands smaller, implying that PC buildings could be designed for smaller lateral seismic forces. The conclusions of this paper are for the particular structural systems and models considered. Much more research is needed to reach more general conclusions. [ABSTRACT FROM AUTHOR]

In this paper, a nonlinear three-dimensional finite element (FE) model for a hybrid sliding–rocking (HSR) column is developed. The HSR columns are segmental members incorporating internal unbonded post-tensioning, rocking joints at the member ends, and intermediate sliding joints along the member height. The HSR columns introduce new design parameters (e.g., frictional properties at the sliding joints, amplitude of joint sliding, number/distribution of sliding joints along the column height) and additional modeling challenges (e.g., contact interactions between adjacent segments and between segments and the internal unbonded post-tensioning tendons) as compared with conventional monolithic or rocking-only members. In the proposed modeling approach, contact interaction amongst adjacent segments and between segments and unbonded tendons are captured. Concrete segments are modeled using solid elements, mild steel reinforcement is modeled by beam elements embedded into the concrete segments, and the unbonded tendons are modeled using truss elements. The FE model was validated against available experimental data and was then used to conduct a parametric pushover study. Variations of the external vertical load were found to have minor effects on the lateral column response. Increase of the initial post-tensioning force resulted in early onset of inelastic response of the tendons, while the peak lateral column strength remained unchanged. Joint sliding increased the lateral deformation capacity of the column. Propagation of sliding from bottom to top and vice versa had small effects on the lateral response of the column. Propagation of sliding was controlled by the friction properties at the sliding joints. [ABSTRACT FROM AUTHOR]

The global ductility parameter $$(\mu _{G})$$ , commonly used to represent the capacity of a structure to dissipate energy, and its effects, considered through the ductility reduction factor $$(R_{\upmu })$$ , are studied for buildings with moment resisting steel frames (MRSF) which are modeled as complex multi degree of freedom systems. Results indicate that the $$\mu _{G}$$ value of 4, commonly assumed, cannot be justified, a value between 2.5 and 3 is suggested. The ductility reduction factors associated to global response parameters may be quite different than those of local response parameters, showing the limitation of the commonly used equivalent lateral force procedure (ELFP). The ratio $$(Q)$$ of $$R_{\upmu }$$ to $$\mu _{G}$$ is larger for the models with spatial MRSF than for the models with perimeter MRSF since their ductility demands are smaller and/or their ductility reduction factors larger. According to the simplified Newmark and Hall procedure, the $$Q$$ ratio should be equal to unity for the structural models under consideration. Based on the results of this study, this ratio cannot be justified. The reason for this is that single degree of freedom systems were used to derive the mentioned simplified procedure, where higher mode and energy dissipation effects cannot be explicitly considered. A value of 0.5 is suggested for $$Q$$ for steel buildings with perimeter MRSF in the intermediate and long period regions. The findings of this paper are for the particular structural systems and models used in the study. Much more research is needed to reach more general conclusions. [ABSTRACT FROM AUTHOR]

Deformation quantities such as strain, curvature and displacement are of paramount importance in seismic design within a performance-based procedure that aims to control the structural response at predefined levels of inelastic action. Given the importance of curvature expressions independent of strength for the design process, and for the particular case of T-shaped walls, the curvature trends at yield, serviceability and ultimate limit state are determined in graphical and analytical form. The comprehensive set of equations proposed in this work are strength independent and allow the reliable computation of limit-state curvatures, essential in a displacement-based design approach, and thus the realistic estimation of appropriate ductility factors in the design of T-shaped walls. Furthermore, results regarding the section properties of T-shaped walls, such as the elastic stiffness and the moment capacity for opposite directions of loading, offer additional information on T-shaped walls. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: Buckling-restrained braces (BRBs), which are braces that do not buckle in compression, have recently become popular for use in the primary lateral-force-resisting systems of structures located in high seismic regions of the United States. Although testing has shown that BRBs possess high ductility capacity, no generally accepted method yet exists to predict the cumulative plastic ductility capacity of a BRB. This research developed ductility capacity models for BRBs using a statistical framework and the results of past experimental studies. The primary outcome of the research is a model with sufficient accuracy for predicting BRB failure in engineering applications. [Copyright &y& Elsevier]

Abstract: This paper presents the development of response spectra plots for inelastic degrading structural systems subjected to seismic excitations. New constitutive models for degrading structures are defined and calibrated against experimental data. A set of earthquake records is selected for the study, and scaling effects of the records are investigated for degrading systems. Incremental Dynamic Analyses of several degrading structures with different material models are conducted in order to evaluate the effect of degradation on the response. These analyses were used to develop relationships for degrading structures. The relationships were subsequently used to construct constant ductility response spectra plots for degrading systems. Finally conclusions regarding the behavior and collapse potential of different structural systems are drawn. [Copyright &y& Elsevier]

• Novel eighteen GMRC and SMRC columns were manufactured. • 3D finite element modeling (FEM) of all specimens was performed. • Mostly GMRC specimens failed in the upper half portion. • FEM predictions were in close correlation with test results. Large quantity of recycled aggregate concrete (RAC) obtained from concrete and demolition waste needs to be disposed of properly and sustainably. The present investigation aims to examine the axial compressive behavior of polypropylene macro synthetic fiber (PMF) reinforced RAC (MRC) columns containing glass fiber reinforced polymer (GFRP) rebars. Nine GFRP rebars reinforced columns (GMRC columns) and nine steel rebars reinforced columns (SMRC columns) with 1200 mm height and 300 mm diameter were tested under concentric and eccentric loading. The axial load-carrying capacity (LC), failure behavior, damaging modes, and compressive deformations were assessed. The results depicted that the SMRC columns had greater axial LC by 23.4% and lower ductility capacity by 16% than GMRC columns. Mostly, the failure mechanism of GMRC and SMRC columns was similar. The application of eccentricity resulted in similar declines in axial LC for both GMRC and SMRC specimens. 3D finite element modeling of GMRC specimens was performed using a modified damaging plastic model for MRC. The suggested finite element model estimated the efficiency of GMRC specimens with high accuracy for both axial LC and corresponding deformations of samples. [ABSTRACT FROM AUTHOR]

Equivalent fixed-based cantilever approach is commonly used for seismic performance-based design of pile foundations supporting marine and bridge structures. In this method, prior knowledge of parameters such as equivalent length of fixity, depth-to-plastic hinge and equivalent plastic-hinge length is essential for reliable assessment of ductility capacity. Available recommendations for these parameters have resulted in contradicting conclusions due to numerical simplifications and/or experimental limitations. In this study, basic concepts of strain wedge model are employed to provide guidelines for the estimation of the key parameters by incorporating nonlinear behavior of the soil-pile system. A set of dimensionless design charts is produced based on an analytical approach covering a range of practical values of soil and pile properties. Finally, the performance of the proposed analytical model in assessing the local curvature ductility of a bridge system induced by an imposed displacement ductility factor is demonstrated through two examples. • Simplified assessment of ductility capacity for extended pile shafts based on equivalent cantilever method. • Estimation of key parameters of equivalent cantilever model incorporating nonlinear behavior of soil-pile system. • Design guidelines for cast-in-drilled-hole (CIDH) reinforced concrete piles using basic concepts of strain wedge model. [ABSTRACT FROM AUTHOR]

The test results described in Part 1 of this paper (Lee and Bruneau, 2008) on twelve steel built-up laced members (BLMs) subjected to quasi-static loading are analyzed to provide better knowledge on their seismic behavior. Strength capacity of the BLM specimens is correlated with the strength predicted by the AISC LRFD Specifications. Assessments of hysteretic properties such as ductility capacity, energy dissipation capacity, and strength degradation after buckling of the specimen are performed. The compressive strength of BLMs is found to be relatively well predicted by the AISC LRFD Specifications. BLMs with smaller kl/r were ductile but failed to reach the target ductility of 3.0 before starting to fracture, while those with larger kl/r could meet the ductility demand in most cases. The normalized energy dissipation ratio, EC/ET and the normalized compressive strength degradation, Cnr/Cr of BLMs typically decrease as normalized displacements δ/δb.exp increase, and the ratios for specimens with larger kl/r dropped more rapidly than for specimens with smaller kl/r; similar trends were observed for the monolithic braces. The BLMs with a smaller slenderness ratio, kl/r, and width-to-thickness ratio, b/t, experienced a larger number of inelastic cycles than those with larger ratios. [ABSTRACT FROM AUTHOR]

Abstract: This paper examines the cyclic performance of axially loaded tubular members used as bracing elements to provide lateral seismic resistance in steel framed structures. An experimental study into the response of members with square and rectangular hollow sections, made from cold-formed steel, is described. Three cross-sectional geometries were employed to represent a range of local and overall slenderness. Fifteen specimens, with normalised slendernesses between 0.4 and 3.2, were tested under cyclic axial displacements of increasing amplitude. In addition, twenty-one short specimens were tested under displacement-controlled monotonic tension loading, focusing primarily on the relationship between the tensile resistance of the material and that of the cross-section. Based on the results obtained in both sets of tests, and with due consideration of existing design provisions, the paper assesses the influence of section and member properties on the structural parameters that are most important for seismic design. These include the tensile capacity, initial and post-buckling compressive resistance, ductility capacity, energy dissipation, and mid-length lateral deformations of bracing members. [Copyright &y& Elsevier]

Abstract: This paper describes an experimental study on the response of hollow and filled steel members to monotonic and cyclic axial loading. Monotonic tests were first performed on short specimens to establish their compressive and tensile axial resistances and to investigate the effect of infill on local buckling and ductility. These were followed by cyclic tests on longer bracing members with three different cross-section sizes. The presence of concrete infill was observed to influence the mode of failure displayed by the specimens, as well as their compression and tension load responses. The ductility capacities of the individual specimens are compared, and the effects of slenderness, steel strength and infill are quantified. The experimental findings are compared with the recommendations of a number of international codes of practice and previous research studies on the seismic response of steel braces. It is found that the infill contributes to the compression resistance of the brace, even after multiple inelastic load reversals, and that it can improve ductility capacity by preventing or limiting local buckling. [Copyright &y& Elsevier]

Strap-braced stud walls are one of the primary lateral-force resisting systems for conventional cold-formed steel (CFS) buildings. While CFS wall-panels in general exhibit a satisfactory seismic performance, previous studies showed that they may experience a premature brittle failure in the presence of vertical loading. However, current design codes do not make any provisions for calculating the lateral load capacity and ductility of strap-braced stud wall frames under vertical loading. This study aims to develop, for the first time, a practical design methodology for seismic design of CFS strap-braced stud wall frames under such conditions. To this end, a comprehensive parametric study was carried out using experimentally validated detailed numerical models in ABAQUS, accounting for material nonlinearities, initial geometric imperfections, and secondary moments due to P-Δ effects. Parameters of the investigations were the strap thickness and the intensity of the vertical loading. Design formulae were derived, and a preliminary design methodology was proposed for predicting the lateral load capacity and ductility of single strap-braced stud walls under a range of vertical loading ratios. The efficiency of the proposed method compared to Eurocode 8 design was then demonstrated for a 6-storey CFS frame, which highlighted the importance of considering the effects of vertical loads in the seismic design of these systems. It was demonstrated that ignoring those factors can lead to a brittle lateral response even if all other code requirements are satisfied, while the proposed design methodology was shown to be efficient to reach the target lateral load and ductility capacities. [Display omitted] • Performance of CFS strap-braced walls investigated under lateral and vertical loads. • Design codes overestimate ductility of CFS walls subjected to high vertical loads. • A framework developed for seismic design of multi-storey CFS strap-braced walls. • The efficiency of the proposed design equations demonstrated for a 6-storey system. • While proposed design provided high ductility, EC design led to brittle failure modes. [ABSTRACT FROM AUTHOR]