AbstractThe use of integral mechanical attachments (IMAs) in spatial free-form timber plate structures has been revitalized by the production of engineered boards and recent developments in digital ...fabrication and computer-aided design. Despite the widespread interest in utilizing such structural systems, there have been very few efforts to develop modeling strategies that can be used by practitioners. Detailed finite-element (FE) models are typically computationally expensive and require advanced expertise. Accordingly, this paper introduces a simplified yet robust macroscopic modeling technique for spatial free-form timber plate structures with IMAs. This approach employs only beam and spring elements to simulate the structural behavior. The macromodel was introduced and the associated mechanical properties were computed. FE models constructed using shell elements and the results from recent experiments performed on a full-scale prototype were used to verify the proposed macromodel. The results showed that the response of the macromodel was closely in line with that of the experiments and FE models. Despite its simplicity, the macromodel is robust and can simulate the behavior of integrally attached timber plates. It was also demonstrated that the computational time for the macromodel is significantly less than the FE simulation.
This paper proposes a new data‐driven method to generate three‐dimensional fragility surfaces for post‐earthquake damage assessment of reinforced concrete (RC) shear walls (SWs) using image‐based ...damage features. A research database comprised of 212 images corresponding to 66 damaged reinforced concrete shear walls tested under quasi‐static cyclic loads is utilized. The walls are categorized into three damage states defined based on different load points along the backbone curve. Convolutional kernel‐based filters are then employed to measure the crack patterns and crushed areas from images of the damaged walls. A set of 360,000 sub‐cracks from the 212 images is analyzed using Gaussian mixture modeling to distinguish between shear and flexural cracking. These two types of cracking, along with crushing, are the prominent characteristics used to determine the damage states of the RCSWs. The extracted features of shear and flexural cracking are also compressed into a unique cracking index using the Principal Component Analysis theory for dimensionality reduction. Using the compressed feature of cracking and crushing, a new methodology for generating three‐dimensional fragility surfaces, entitled the Box‐counting method, is introduced, and the damage surfaces are developed based on visual damage features. The damage surfaces are finally formulated using statistical models or machine learning regression learners. The proposed fragility surface can be used for post‐earthquake damage state identification, risk assessment, and loss estimation of damaged RCSWs.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
AbstractA seismic risk assessment of a 42-story reinforced concrete dual-system building considering mainshock and aftershock hazard is presented. Sequential nonlinear response history analyses are ...performed using as-recorded mainshock-aftershock sequences. Aftershock assessment describes the case where the mainshock has occurred, and the associated damaged state of the building is known. A Markov process model is used to integrate the increase in vulnerability of the mainshock-damaged building with the time-dependent aftershock hazard. Aftershock risk is quantified as the probability of exceeding the structural response demand limits used in performance-based seismic design of tall buildings at different instants in time following the mainshock. The same metric is used to quantify mainshock-aftershock risk; however, for this type of assessment, the uncertainty in the intensity and damage caused by both the mainshock and aftershock is considered. The results of mainshock-only, aftershock, and mainshock-aftershock assessment show that the coupling beam rotation demand limit generally has the highest probability of exceedance compared with the peak transient and residual story drift ratios, frame beam rotations, and compressive and tensile strain in boundary element concrete and steel, respectively. The implied 50-year exceedance probabilities of the demand limits currently used for the collapse prevention performance level were found to vary significantly across the various response parameters.
•Parameterized fragilities developed for a controlled rocking steel braced frame.•Fragility functions describe probability of exceeding system-level limit states.•Surrogate models link structural ...response to shaking intensity and design variables.•Immediate occupancy is controlled by fuse deformation and peak residual drifts.•Frame aspect ratio has the greatest influence on overall performance.
Parameterized fragility functions are developed for a controlled rocking steel braced frame (CRSBF) system, which link the probability of exceeding system-level limit states to ground motion intensity and design parameters such as frame aspect ratio, the initial post-tensioning force, the yield force in the fuse element and the dead load on the frame. The considered building performance levels include immediate occupancy (IO), repairability (RP), and collapse prevention (CP), which are achieved through non-exceedance of predefined response demand thresholds. Surrogate models are developed to predict the statistical distribution of global (peak transient and residual story drift) and local (posttensioned element strain and fuse deformation) response demand parameters using the ground motion intensity and CRSBF design variables as input parameters. The surrogate models are coupled with Monte Carlo simulations to develop the parameterized fragility functions, while incorporating model parameter uncertainty. The procedure is demonstrated using a 6-story CRSBF building. The results show that the IO and CP performance levels are controlled by the demand thresholds for peak transient story drifts. Among the four design parameters considered in this study, the aspect ratio had the greatest influence on the CRSBF performance. However, when measured in terms of the conditional probability of not meeting or exceeding the performance level at the maximum considered earthquake hazard level, the effect is significantly reduced for higher (better) performance levels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
AbstractModels for reconstructing seismic response demands across multiple buildings can aid in cluster-level rapid postearthquake damage assessment. Response demands from 188 buildings affected by ...25 earthquakes were used to develop a cross-building response reconstruction model. A structural response prediction model (SRPM) was developed, which is based on a modern ground motion model with added “building response” terms. A kriging algorithm is used to interpolate the within-event residuals which, together with the SRPM, form a generalized cross-building response reconstruction (CBRR) model. Given the recorded responses for a subset of instrumented buildings in a cluster, the demands in the uninstrumented buildings can be reconstructed by combining the median values generated from the SRPM and estimated within-event residuals for a given site obtained from the kriging model.
•A probabilistic approach to evaluating combinations of orthogonal seismic demands.•Methodology applied to 3-, 6- and 9-story special concentric braced frames.•Combinatorial effects most influenced ...by building height and force demand level.
A probabilistic approach to assessing the effectiveness of the rules used to combine demands from orthogonal ground motion components is developed. Full probability distributions of the ratio between the force demands obtained from nonlinear response history analyses using bidirectional loading, which are taken as the “true” demands, and rule-based combinations of the demands from unidirectional loading, are developed. For the percentage combination rules (100-p), a relationship is established between the value of p (e.g. p = 30% for 100–30 rule) and the probability that the bidirectional loading demands exceed the rule-based combination of the unidirectional loading demands. Using this relationship, an appropriate value of p based on an acceptable exceedance probability is determined. The proposed framework is demonstrated using special concentric braced frames with biaxially loaded columns, which are shared by orthogonal braced frames. The combinatorial effect of the orthogonal responses is found to be influenced by several factors including the type of demand parameter (e.g. column axial forces versus stresses), demand level and building height.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
A performance-based methodology is presented to quantify the reduction in collapse safety of main shock-damaged reinforced concrete frame buildings with infills. After assessing their collapse safety ...in the intact state, the residual collapse capacity following main shock damage is evaluated by conducting incremental dynamic analysis to collapse using main shock-aftershock ground motion sequences. The median collapse capacity and conditional probability of collapse for the main shock-damaged building, normalized by that of the intact case are the metrics used to measure the reduction in collapse safety. Taller buildings with built-in soft and weak first stories have the highest reduction in collapse safety as a result of main shock damage. Among the engineering demand parameters recorded during the main shock analyses, story drift demands (peak transient and residual) and infill strut axial deformations have the highest correlation with the decline in collapse performance. The results of the main shock-aftershock incremental dynamic analysis to collapse are used to develop fragility functions for the limit state defined by the building being structurally unsafe to occupy.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
The relationship between the earthquake performance of an inventory of buildings and the seismic resilience of a residential community is examined, by quantifying the immediate post-earthquake ...reduction and recovery of the shelter-in-place housing capacity. The effect of several mitigation strategies that involve replacing portions of the existing building stock with an enhanced seismic performance system is evaluated. The impact on community resilience is assessed based on the immediate and cumulative loss of permanent housing occupancy as well as the time to recover some fraction of the pre-earthquake housing capacity. The results show how the slope of the recovery curve for occupiable housing during different periods following the event can be linked to the distribution of building damage. In addition to limiting major damage, enhanced building seismic performance is shown to reduce aggregate losses over the recovery period, thereby having a significant effect on both the safety and resilience of residential communities.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
Historical data play a primary role in reconstructing building seismic responses and assessing damage in near-real time. While these types of data sets exist, they are often fragmented, difficult to ...access, and require significant manual manipulation on the part of the user to obtain useful information. This article introduces a relational database that comprises historical data from 216 buildings subjected to M>4 earthquakes, spanning a 36-year period in California. It includes comprehensive information about the events and accelerometer-equipped buildings, parameters that are often used in post-earthquake impact assessments, and time-series structural response data recorded during real earthquakes. The database is designed to facilitate incremental updating as new events occur, and the associated data becomes available. It is also paired with a Python-based tool that reduces the barrier to user access with a few simple inputs. The long-term goal is to expand the database to include additional seismic events and spur the development of similar single- or multi-hazard repositories.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
Summary
A methodology is introduced to assess the post‐earthquake structural safety of damaged buildings using a quantitative relationship between observable structural component damage and the ...change in collapse vulnerability. The proposed framework integrates component‐level damage simulation, virtual inspection, and structural collapse performance assessment. Engineering demand parameters from nonlinear response history analyses are used in conjunction with component‐level damage simulation to generate multiple realizations of damage to key structural elements. Triggering damage state ratios, which describe the fraction of components within a damage state that results in an unsafe placard assignment, are explicitly linked to the increased collapse vulnerability of the damaged building. A case study is presented in which the framework is applied to a 4‐story reinforced concrete frame building with masonry infills. The results show that when subjected to maximum considered earthquake level ground motions, the probability of experiencing enough structural damage to trigger an unsafe placard, leading to building closure, is more than 2 orders of magnitude higher than the risk of collapse.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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