•Yielding of slab reinforcement registered prior to yielding of wall reinforcement.•The drift capacity of the building was inversely related to the slab reinforcement.•Models with linear slabs did ...not predict precisely the response of a nonlinear model.•Shear forces transferred through the slabs vary notably the axial load of the walls.
Reinforced concrete (RC) structural walls are widely used in high-rise buildings as the lateral force resisting system because of their inherent economy, stiffness, and strength. The floor plan configuration of residential buildings in Chile consists mainly in assemblies of large longitudinal walls and shorter transverse walls coupled by floor slabs. The coupling effect of the slabs has affected the response and the observed damage of RC buildings in recent earthquakes. The main objective of this article is to assess the seismic response of a RC structural wall building with coupling slabs. Additionally, the effect of the amount of slab reinforcement on the seismic response of the building is evaluated. To achieve the proposed objectives, seven three-dimensional models of a case study building were developed using shell-type elements in DIANA. The first four models aim to evaluate the effect of using elastic slabs with reduced (i.e. cracked) moment of inertia. The last three models consider nonlinear behavior for both walls and slabs. The response of the building was estimated using nonlinear static analysis and the seismic performance is evaluated from the results of roof displacement and shear, moment, and axial forces of the walls. Additionally, the seismic performance is evaluated from the strain demands of concrete and steel in both walls and slabs. Relevant conclusions about the building behavior, slab demands, and failure mode are drawn.
•Performance of shear wall buildings was improved by increasing the lateral stiffness.•Larger stiffness reduced the probability of exceeding life safety limit state.•Larger stiffness reduced the ...probability of collapse for the same IM.•Larger stiffness increased the probability of collapse in 50 years.•Displacement ductility increased when the stiffness of the building decreased.
This study assesses the effect of the stiffness on the seismic performance of residential shear wall buildings designed according to current Chilean regulations, including DS60 and DS61. Specifically, the paper focuses on the effect of stiffness on the building overstrength, displacement ductility, fragility for Life Safety (LS) and collapse limit states, as well as the probability of achieving these two limits states in 50 years. The seismic performance is assessed for a group of four 20-story residential shear wall buildings archetypes located in Santiago. Walls were modeled using the multiple vertical line element model (MVLEM) with inelastic hysteretic materials for the vertical elements, and a linear-elastic shear behavior. Pushover analyses were considered to estimate the buildings overstrength and displacement ductility, while incremental dynamic analyses were performed to estimate fragility curves. A probabilistic seismic hazard analysis, which considered the seismicity of Chile central zone, was performed to estimate the probability of achieving the two limits states in 50 years. The results show that an increase in the stiffness reduces the chance of exceeding the LS and collapse limit states for the same intensity level. Additionally, the probabilistic seismic hazard analysis shows that, when the stiffness increases, the probability of reaching the LS limit state in 50 years also decreases. Counterintuitively, the probability of collapse in 50 years increases as the stiffness increases, due to the considered seismic hazard and the design requirements. Since society is moving towards resilient structural designs that minimize damage, disruption and economic losses, it is concluded that the performance of reinforced concrete shear wall buildings is improved by increasing the stiffness.
•Asymmetric bridge characteristics generate deck rotation in straight bridges during an earthquake.•The studied asymmetries predicted part of the deck rotation observed after the 2010 earthquake.•The ...seismic demand of the lateral stoppers influenced the deck rotation and the bridge behavior.•The diaphragm reduced the deck rotation and improved the behavior of the bridge.
The 2010 Maule and 2015 Illapel earthquakes recently affected the highway infrastructure in Chile. Deck rotation in straight and skewed bridges, damage to the connection between the superstructure and substructure, and even collapse of bridges were observed in these events. However, deck rotation in straight bridges has been identified as an unusual failure mode. The main objective of this research is to evaluate if potential asymmetries in the bridge characteristics can be a probable reason that explain deck rotation observed in straight bridges. The second objective is to assess the effect of transverse diaphragms on the seismic behavior of these bridges. In order to achieve these objectives, the Chada underpass, which suffered deck rotation, damage to lateral stoppers and prestressed concrete girders during the Maule earthquake, is used as a case study. The asymmetries considered in this study are related to the variation of the strength of the lateral stoppers, the coefficient of friction of the elastomeric bearings, and the gap distance between the lateral stoppers and prestressed concrete girders. The induced asymmetries are evaluated with a three-dimensional model of the bridge developed in Opensees. The seismic response of the bridge is obtained from nonlinear dynamic analyses considering seven seismic records applying both horizontal components simultaneously. From the results of this study, it is concluded that the studied asymmetries induce deck rotations that can explain only part of the observed deck rotation in the studied straight bridge. A maximum relative horizontal displacement of the deck of 58.2 cm was estimated for the case with asymmetric strength of lateral stoppers, which is only 41% of the residual relative displacement measured in Chada bridge after the Maule earthquake. Additionally, it is concluded that the incorporation of transverse diaphragms, which is required by current Chilean bridge design code, improved the seismic behavior of the studied bridge.
•Fragility curves are obtained for typical non-skewed highway bridges in Chile.•The seismic effect of seismic bars is assessed experimentally.•The fragility curves are validated with statistical ...damage from 2010 Chile earthquake.•The transverse seat width in bridges is critical to reduce the probability of collapse.
Recent earthquakes in Chile and worldwide have caused significant economic losses due to the damage on the road bridge network. To conduct seismic risk assessment studies and to improve resilience of bridges, seismic vulnerability studies are required. The main objective of this study is to construct fragility curves of typical non-skewed highway bridges in Chile. The fragility curves are obtained from an incremental dynamic analysis of a two-dimensional model of the bent cap of a two-span simply supported underpass. As most bridges are constructed with seismic tie-down bars, their constitutive behavior was obtained experimentally. A total of five seismic bar specimens were tested to characterize their cyclic behavior in bridges with and without transverse diaphragms. The incremental dynamic analysis was performed with the two horizontal components of seven seismic records obtained from the Mw 8.8, 2010 Chile earthquake. Additionally, a parametric study is conducted to assess the seismic behavior of bridges with different configurations of seismic bars, with lateral stoppers, and with varying length of the transverse seat width. Results from this study reveal that seismic bars have a limited contribution to the seismic performance of the studied bridge, especially when lateral stoppers are incorporated. Additionally, the transverse seat width is found to be critical to reduce the collapse probability of the superstructure. The provided fragility curves may be used for seismic risk assessment and to evaluate possible improvements in seismic bridge design codes.
•Damage in RC walls during 2010 earthquake is related to high axial loads.•The compressive-flexural failure mode observed in walls during 2010 Chile earthquake is reproduced experimentally.•High ...axial load triggers a brittle failure and decreases wall displacement capacity.•In walls with high axial load failure occurred immediately after concrete spalling.
About 2% of Reinforced Concrete (RC) buildings taller than nine stories suffered serious damage in structural walls during the 2010 Chile earthquake. The observed damage involved mostly crushing of concrete, buckling of vertical reinforcement, and opening of the horizontal reinforcement. This damage is attributed to poor concrete confinement in the web and boundaries, inadequate horizontal reinforcement detailing, and high axial loads. This research aims to reproduce the observed damage and evaluate the influence of axial loads in the seismic behavior of RC walls with unconfined boundaries. To achieve these objectives, three identical wall specimens were tested. The wall specimens were designed with characteristic wall detailing obtained from data of five damaged buildings. These wall specimens were tested under equal lateral displacement cycles and subjected to different axial load ratios. The flexural-compressive failure mode exhibited by damaged walls during the earthquake was reproduced in these tests. Experimental results indicate that high axial load has a significant effect on the seismic performance and failure mode of RC walls. Indeed, it triggers a dangerous brittle concrete crushing failure which occurs immediately after spalling of the concrete cover.
•Losses of stiffer buildings resulted higher because of their higher seismic hazard.•Losses for the studied buildings are less than estimated for RC frame buildings.•Losses are mainly due to the ...cases of non-collapse.•Repair costs of partitions contributed the most to the total loss of the buildings.
This research paper evaluates the effect of lateral stiffness on expected economic losses in reinforced concrete shear wall buildings designed following current Chilean standards, including DS60 and DS61. Economic losses were evaluated for a group of four 20-story archetype buildings located in Santiago, Chile. The methodology developed by the Pacific Earthquake Engineering Research Center was considered to estimate economic losses. The expected annual loss (EAL) and the present value (PV) of the losses in 50 years were used as measures of economic loss. A probabilistic seismic hazard analysis, which considered the seismicity of central Chile, was performed to estimate both metrics. The results show that when the lateral stiffness of the building increases, the EAL also increases. This implies that stiffer buildings are more vulnerable from an economic point of view. This counter-intuitive finding results from the higher seismic hazard of stiffer buildings and the minimum design base shear required by DS61 that governed the design of the studied buildings. Additionally, it was found that the EAL and the PV of losses in 50 years for the four archetypes do not exceed 0.3% and 7.8% of the total construction cost of the buildings, respectively. These monetary losses are relatively low, which is consistent with the outstanding seismic performance of reinforced concrete shear wall buildings.
•Six ½-scale slender reinforced concrete walls were tested.•The compressive-flexural failure mode observed in walls during 2010 Chile earthquake was reproduced experimentally.•A 25% thickness ...reduction decreased the ultimate displacement and energy dissipation capacity of the tested walls.•Closed stirrups at the boundaries reduced the likelihood of out-of-plane buckling of a wall.
Residential reinforced concrete buildings performed well during the 2010 Mw 8.8 Maule, Chile earthquake. However, brittle damage was observed in reinforced concrete structural walls. The most frequent observed damage in such walls was crushing of concrete due to flexural-compressive interaction, buckling and fracture of longitudinal reinforcement, and opening of the horizontal reinforcement. The main objective of this study is to understand the observed damage in slender walls after 2010 Maule earthquake and to reproduce and analyze experimentally the seismic behavior of such walls. The second objective is to provide recommendations to estimate the lateral displacement and the effective stiffness of slender walls. To achieve these objectives, six ½-scale slender reinforced concrete walls were tested using a conventional quasi-static cyclic incremental lateral displacement test protocol with a constant axial load. The test results are compared to a reference wall tested previously in the same research project. The variables analyzed in this study are: wall thickness, wall aspect ratio, use of uniformly distributed vertical reinforcement, detailing of 135-degree hooks for the horizontal reinforcement, addition of closed stirrups in the wall boundaries, and addition of transverse cross-ties. The observed damage in the tested walls was similar to that observed in walls of buildings damaged during the 2010 Maule earthquake. The behavior of the tested walls was dominated by bending due to their relatively large aspect ratio. The failure, determined by the loss of ability to carry axial load, occurred suddenly as a compression failure along the entire cross section at the base of the tested walls. Test results showed that a 25% reduction in wall thickness reduced the ultimate displacement capacity, ductility, and energy dissipation ability of the wall. Closed stirrups and cross-ties were effective in increasing displacement capacity and ductility, and closed stirrups were effective in preventing out-of-plane buckling of the wall after compression failure. The average effective stiffness ratio of the tested walls was 0.39, which is slightly larger than the ACI 318 suggestion of 0.35.
•Structural information of 36 R/C buildings damaged during the 2010 earthquake.•Buildings had low wall thickness, vertical irregularity, and were new (<10years).•Average gravity axial stresses were ...2.39MPa and average ALR were 10.4%.•Dynamic amplification of axial loads in walls ranges from 1.3 to 2.9.•A simplified procedure is proposed to estimate seismic axial loads in RC walls.
This research article investigates the correlation between a suite of global structural parameters and the observed earthquake responses in 43 reinforced concrete shear wall buildings, of which 36 underwent structural damage during the Mw 8.8, 2010, Maule earthquake. During the earthquake, some of these buildings suffered brittle damage in few reinforced concrete walls. Damage concentrated in the first two building stories and first basement, and most typically, in the vicinity of important vertical irregularities present in the resisting planes. This research consolidates in a single database information about these 36 damaged buildings for which global geometric and building design parameters are computed. Geometry related characteristics, material properties, dynamic and wall-related parameters, and irregularity indices are all defined and computed for the inventory of damaged buildings, and their values compared with those of other typical Chilean buildings. A more specific comparison analysis is performed with a small benchmark group of 7 undamaged buildings, which have almost identical characteristics to the damaged structures, except for the damage. A series of ordinal logistic regression models show that the most significant variables that correlate with the building damage level are the region where the building was located and the soil foundation type. Most of the damage took place in rather new medium-rise buildings, and was due in part to the use of increasingly thinner unconfined walls in taller buildings subjected to high axial stresses due to gravity loads, which in turn are increased by dynamic effects. Time–history analyses are performed in five damaged buildings to analyze in more detail the dynamic effect in these amplifications of the average axial load ratios. Finally, a simplified procedure to estimate this dynamic amplification of axial loads is proposed in these buildings as an intent to anticipate at early stages of the design the seismic vulnerability of these structures.
About 2 % of reinforced concrete (RC) buildings taller than nine stories suffered important structural damage during 2010 Chile earthquake. The typical structural configuration of residential ...buildings is characterized by a large number of RC structural walls which provides high lateral stiffness and strength. The first objective of this paper is to obtain global geometric and design parameters of RC structural walls in damaged buildings and correlate their values with the observed damage. The second objective is to compare the roof displacement capacity with the roof displacement demand in critical walls, and hence, try to explain the observed damage. The wall parameters were obtained from five representative damaged structural wall buildings; these are: wall thickness, aspect ratio, axial load, reinforcement ratios, and the ratio between horizontal reinforcement spacing and the vertical bar diameter. The roof displacement capacity is obtained using a plastic hinge approach, and the ACI 318-08 approach, since both methods are proposed in the current Chilean seismic code. The displacement demand is estimated from ground motions recorded in the vicinity of the buildings. It is found that values of wall parameters correlate well with the observed damage. The structural walls were subjected to relatively high axial loads, and some walls included a large amount of vertical reinforcement to provide the required strength, but had inadequate transverse reinforcement thus compromising ductility. Findings from this research suggest that the plastic hinge approach is inadequate to estimate the roof displacement capacity and lacks correlation with the observed damage. Moreover, the use of the ACI 318-08 approach to estimate the roof displacement capacity is also inadequate, but leads to better predictions of wall displacement capacity. As shown by the results of response history analysis, the failure of walls was triggered by high axial loads rather than flexural deformation.
Introduction: This study assessed the external validity of all published first trimester prediction models for the risk of preeclampsia (PE) based on routinely collected maternal predictors. ...Moreover, the potential utility of the best-performing models in clinical practice was evaluated. Material and Methods: Ten prediction models were systematically selected from the literature. We performed a multicenter prospective cohort study in the Netherlands between July 1, 2013, and December 31, 2015. Eligible pregnant women completed a web-based questionnaire before 16 weeks’ gestation. The outcome PE was established using postpartum questionnaires and medical records. Predictive performance of each model was assessed by means of discrimination (c-statistic) and a calibration plot. Clinical usefulness was evaluated by means of decision curve analysis and by calculating the potential impact at different risk thresholds. Results: The validation cohort contained 2,614 women of whom 76 developed PE (2.9%). Five models showed moderate discriminative performance with c-statistics ranging from 0.73 to 0.77. Adequate calibration was obtained after refitting. The best models were clinically useful over a small range of predicted probabilities. Discussion: Five of the ten included first trimester prediction models for PE showed moderate predictive performance. The best models may provide more benefit compared to risk selection as used in current guidelines.
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