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The failure mode of concrete columns in subway stations during seismic events can be affected by the dynamic fluctuation of the axial forces. This study conducted quasi-static tests with bidirectional loading on three scaled rectangular columns to investigate the influence of highly variable axial compression ratio (ACR). A detailed analysis was conducted of the impact of the highly variable ACR on the column failure mode, reinforcement strains, and hysteretic behavior, and the repairability assessment was discussed. Numerical analysis of the effect of ACR variations was carried out based on the experimental results. In these experiments, the failure modes of central columns in Dakai Station, Japan, during the Kobe earthquake were reproduced, and three columns exhibited compressive-bending-shear damage and compressive-bending damage. As the ACR varied up to three cycles during one horizontal loading cycle, the hysteresis curve of the columns exhibited notable asymmetry. Furthermore, with a large variation of ACR amplitude, the stirrups of the column were fractured due to excessive shear effects. The bearing capacity, energy dissipation, and stiffness degradation of the columns were significantly adversely affected. A reparability assessment of the columns, based on the distribution of reinforcement strains, residual displacements, and concrete damage, is proposed. The effects of varying frequency and amplitude of different vertical ACRs on the hysteretic behavior of columns were analyzed numerically. [ABSTRACT FROM AUTHOR]

While the use of cross-laminated timber (CLT) panels for building construction has increased over the last several decades, current standards and existing literature provide limited information regarding the design of CLT diaphragms or the prediction of their deflections when subjected to wind and strong earthquake motions. This paper presents the design and assessment of a CLT diaphragm that was part of a full-scale two-story structure subjected to shake-table testing. An analytical model is proposed for diaphragm deflection accounting for in-plane shear and bending stiffness, as well as the stiffness of various connections. Moreover, a refined numerical modeling strategy is proposed in order to consider phenomena such as panel-to-panel gap closure. Results indicate that the analytical model yields conservative results both in terms of deflections and forces when compared to the numerical model that simulates similar sources of strength and stiffness. The analytical model is suitable for the design of symmetric diaphragms with regular shapes, whereas the numerical model can also be used to model asymmetric diaphragms with irregular shapes. [ABSTRACT FROM AUTHOR]

A method to calculate structural functionality for building structures based on structural natural frequency was proposed for seismic loading events. Structural functionality loss and recovery were determined by monitoring the change of structural natural frequency during the earthquake events or repair activities. A shape factor was introduced, structural functionality recovery function (SFRF), to consider the repair strategy and repair speed. As an example, this method was applied to obtain the structural functionality curve and seismic resilience of a half scale two-story reinforced concrete (RC) frame structure. This structure was subjected to a series of ground motions on a shake table and then repaired by carbon fiber cloth a total of four times. The results indicate that the SFRF is able to capture the recovery trend of a structure in the repair process. Meanwhile, a damage index-repair target (DI-RT) curve, representing the 5% difference between the proposed and traditional SFRFs, was used to investigate the impact of structural damage degree and repair target. The areas above the curve indicates that the difference between the proposed and traditional SFRFs cannot be ignored. [ABSTRACT FROM AUTHOR]

The safety of railway vehicles running on bridges needs to be evaluated in the seismic design of bridges. This study examined the spectral intensity calculated from the lateral vibration of the bridge deck during earthquakes, a Japanese code-based index to measure bridge vibration's strength. In addition, the effect of the torsion of the bridge deck on vehicle derailment is investigated using a nonlinear vehicle–track–bridge model. The bridge deck torsion increases the derailment risk, especially for bridges with a low natural frequency. The reason lies in that the lateral and torsional deck motions are highly correlated for bridges with lower frequency. Based on this observation, a code-type formula was proposed to evaluate the vehicle running safety including both lateral and torsional motions of the bridge deck. The accuracy of the proposed formula was demonstrated by comparison with vehicle–track–bridge simulation excited by ground motion records. The new procedure overcomes the non-conservative assessment of derailment caused by ignoring bridge torsion. [ABSTRACT FROM AUTHOR]

Displacement-based seismic design often requires nonlinear time history simulation of building responses which is computationally intensive. This technical note presents an artificial neural network (ANN) designed to generate max inter-story drift for buildings with post-tensioned mass timber (MT) rocking walls systems. This particular lateral system was selected because it is an innovative system with limited physical design parameters, making it an ideal candidate for ANN. The proposed model achieved significantly higher computational efficiency than time history simulation, while maintaining similar level of accuracy. The proposed method could potentially be used for automated design of MT rocking wall lateral systems. [ABSTRACT FROM AUTHOR]

With two producers in operation and over 20 buildings already constructed or in planning process, use of cross-laminated timber (CLT) is gaining popularity in Canada. Since CLT as a structural system is currently not included in the National Building Code of Canada (NBCC), one of the most important issues are the values for the force modification factors for seismic design of CLT structures when NBCC equivalent static force procedure is used. In this study, a test-calibrated numerical model for CLT shear walls was applied to develop the design resistances for typical CLT wall configurations. An estimation of a possible range of [R.sub.d]-factors was obtained by developing design variations for three multi-storey CLT apartment buildings. By specifying the desired seismic performance in terms of inter-storey drift, it is concluded that an Rd-factor of 2.0 will likely provide desirable building performance during the design earthquake level event in Vancouver, B.C. Key words: cross-laminated timber, force modification factors, [R.sub.d]-factor, mid-rise building, seismic design, NBCC. Avec deux producteurs en operation et plus de 20 batiments deja construits ou au stade de planification, l'utilisation des poutres stratifiees croisees (CLT) gagne en popularite au Canada. Puisque les CLT ne sont pas incluses dans le Code national du batiment du Canada (CNBC) en tant que systeme structural, l'une des plus importantes questions est les valeurs des facteurs de modification des forces pour la conception sismique des structures en CLT lorsque la procedure de force statique equivalente du CNBC est utilisee. Dans la presente etude, un modele numerique etalonne par essais pour des murs de contreventement en CLT est utilise pour developper les resistances de calcul pour des configurations typiques de murs en CLT. Une estimation d'une plage potentielle des facteurs Rd a ete obtenue en developpant des variations de calcul pour trois immeubles a appartements de plusieurs etages avec structure en CLT. En specifiant le rendement sismique desire en termes de deplacement inter-etage, nous avons conclu qu'un facteur Rd de 2,0 fournira probablement le rendement desire de l'immeuble durant un seisme de calcul du niveau ressenti a Vancouver, C.-B. [Traduit par la Redaction] Mots-cles: poutre stratifiee croisee, facteurs de modification de force, facteur Rd, immeuble de moyenne hauteur, calcul sismique, CNBC., Introduction Cross-laminated timber (CLT) was first developed some 20 years ago in Austria and Germany. European experience shows that this mass timber panelized system can be competitive not only in [...]

In July 2009, a full-scale midrise light-frame wood apartment building was subjected to a series of earthquakes at the word's largest shake table in Miki, Japan. This article focuses on the test results of that full-scale six-story light-frame wood building. The objectives of the testing program were to (1) demonstrate that the performance-based seismic design procedure developed as part of the NEESWood project worked on the full-scale building, i.e., validate the design philosophy to the extent one test can and (2) gain a better understanding of how midrise light-frame wood buildings respond, in general, to a major earthquake while providing a landmark data set to the seismic engineering research community. The building consisted of l,350 [m.sup.2] (14,000 [ft.sup.2]) of living space and had 23 apartment units; approximately one-half one-bedroom units and one-half two-bedroom units. The building was subjected to three earthquakes ranging from seismic intensities corresponding to the 72-year event to the 2,500-year event for Los Angeles. In this paper, the construction of the NEESWood Capstone Building is explained and the resulting seismic response in terms of base shears, selected wall drifts, global interstory drifts, accelerations, hold-down forces, and roof drifts are presented. Detailed damage inspection was performed following each test and those results are summarized also. The building performed excellently with little damage even following the 2,500-year earthquake. The global drift at roof level was approximately 0.25 m and maximum interstory drifts were approximately 2% for the floor average with individual wall drifts reaching just over 3% in one corner of the building at the fifth story. DOI: 10.1061/(ASCE)ST.1943-541X.0000222 CE Database subject headings: Shake table testing; Seismic tests; Earthquake; Frames; Buildings, multistory. Author keywords: Shake table testing; Seismic tests; Earthquake; Woodframe; Light-frame wood; Midrise building.

In July 2009, a full-scale six-storey platform wood frame apartment building was subjected to a series of earthquakes at the world's largest shake table in Miki, Japan. Two double-midply shear wall stacks were installed in the building from the first storey through to the fifth storey. A continuous anchor tie-down system (ATS) was used to prevent overturning and allow the shear walls to develop their full lateral load capacities. This paper focuses on the behavior of the stacked double-midply shear wall in a full-scale midrise building during a series of triaxial shakes scaled for the city of Los Angeles, California. The stacked midply shear wall achieved a maximum interstorey deformation of 40.4 mm (equivalent to 1.64% drift). The uplift forces measured at the bottom storey of the stacked wall exceeded 760 kN, indicating the need for substantial tie-down systems for this type of wall when utilized in a midrise platform wood frame building. Key words: shake table testing, seismic tests, earthquake, wood frame, light-frame wood, midply wall. En juillet 2009, un immeuble residentiel a charpente en bois a plateforme de six etages a plein echelle a ete soumis a une serie de seismes sur la plus grande table de vibration au monde a Miki, au Japon. Deux empilements de murs de contreventement a doubles contreplaques au centre ont ete installees dans l'immeuble du premier jusqu'au cinquieme etage. Un systeme d'ancrage a fixation continue (<< ATS >>) a ete utilise; pour prevenir le renversement et permettre aux murs de contreventement de developper leur pleine capacite de porter la charge laterale. Le present article porte sur le comportement d'un mur de contreventement empile a doubles contreplaques dans un immeuble de hauteur moyenne a pleine echelle durant une serie de secousses triaxiales mises a l'echelle pour la Ville de Los Angeles, Californie. Le mur empile; de contreventement a doubles contreplaques au centre a atteint une deformation maximale de 40,4 mm entre les etages (equivalent a une derive de 1,64 %). Les forces de soulevement mesureees a l'etage inferieur du mur empile ont depasse 760 kN, indiquant le besoin d'avoir des systemes de fixation importants pour ce type de mur lorsqu'il est utilise; dans un immeuble de hauteur moyenne a charpente de bois a plateforme. Mots-cles: essais sur table de vibration, essais sismiques, seisme, charpente de bois, charpente legere en bois, mur a doubles contreplaques au centre. [Traduit par la Redaction], Introduction Platform wood frame construction has been the dominant type of construction for low-rise residential buildings in North America for many decades. With wood shear walls as the primary lateral [...]

This paper presents a simplified direct displacement design (DDD) procedure which was used to design the shear walls for a six-story woodframe structure. The building was tested in the final phase of a Network for Earthquake Engineering Simulation (NEES) project. Specifically, NEESWood Capstone Building was designed to meet four performance expectations: damage limitation, life safety, far-field collapse prevention (CP), and near-fault CE The performance expectations are defined in terms of combinations of interstory drift limits and prescribed seismic hazard levels associated with predefined nonexceedance probabilities. To verify that design requirements were met, a series of nonlinear time-history analyses (NLTHAs) was performed using suits of both far-field and near-fault ground motion records. The distributions of interstory drifts obtained from the NLTHA confirm that the Capstone Building designed using DDD meets all four target performance expectations, thereby validating the DDD procedure. Additionally, collapse analysis in accordance with the recently proposed Applied Technology Council project 63 (ATC-63) methodology was performed. The results of incremental dynamic analyses confirmed that the Capstone Building designed using the DDD procedure has adequate capacity margin against collapse, as dictated by the ATC-63 methodology. DOI: 10.1061/(ASCE)ST.1943-541X.0000181 CE Database subject headings: Displacement; Wood structures; Structural design; Shear walls; Earthquake engineering; Seismic effects. Author keywords: Displacement-based design; Wood structures; Shear walls; Earthquake engineering; Seismic hazard; Structural engineering; Performance-based design.

The experimental seismic responses of a full-scale two-story light-frame wood townhouse building, designed to modern U.S. engineered seismic design requirements, were compared against the predictions of a new software package entitled seismic analysis package for woodframe structures (SAPWood) developed recently within the NEESWood Project. The main objective of this paper was to verify the accuracy of the predictions from the SAPWood model, which incorporates shear deformations of shear walls as well as cumulative floor displacements caused by the out-of-plane rotations of the floor and ceiling diaphragms. A comparison was conducted on interstory drifts and shear wall deformations for various structural configurations (construction phases) of the test building and excitation levels. Good agreement was found between the numerical predictions and test results for the four different construction phases. The SAPWood model was shown to be a promising numerical tool for predicting the seismic response of light-frame wood structures. DOI: 10.1061/(ASCE)ST.1943-541X.0000086 CE Database subject headings: Seismic analysis; Numerical models; Earthquakes; Frames; Wood structures; Computer software. Author keywords: Seismic analysis; Numerical model; Time history; Earthquakes; Wood structures.

With recent developments of engineered wood products such as cross laminated timber, mass timber buildings in areas of high seismicity are becoming feasible and offer benefits such as faster construction and unique architectural features. It has also opened the door to creating seismically resilient lateral systems that sustain minor and reparable damage during large earthquakes. This paper presents a numerical modeling procedure for mass timber rocking wall lateral system with distributed spring elements to model base rocking. This modeling technique was validated by comparing the behavior with results from the full‐scale two‐story shake table test on a mass timber building with coupled CLT rocking walls completed as part of the NHERI TallWood Project. Although the lateral system performed better than expected during testing, it was determined that the flexibility of the foundation actually limited damage to the rocking wall panels. By adjusting the numerical model to represent a rigid foundation boundary condition, it was determined that the wall system would have experienced more damage, but would have still met design performance objectives had it been tested on a rigid foundation. [ABSTRACT FROM AUTHOR]

Performance-based seismic design (PBSD) of wood frame structures has been only preliminarily investigated by a handful of researchers around the world and is currently under development in the United States as well as other countries worldwide. This paper presents the basic concept of applying system identification logic as one alternative for PBSD of wood frame structures. In PBSD of wood frame structures, one prescribes combinations of hazard level and corresponding performance, and 'designs' the system such that these performance metrics ate met. For wood frame buildings this procedure fits the definition of a system identification problem, i.e., the input and output are known and the nonlinear system between them is sought. In most cases the shearwall locations, i.e., geometry, are known, and only the wall design is sought. In this papel the concept is presented and a procedure to apply it within a PBSD framework is proposed. The validity of the procedure is confirmed through two illustrative examples, namely the design for a two-story wood shearwall and a two-story wood frame building. An existing ten-parameter hysteresis model commonly used for seismic analysis of wood frame structures was used in both examples to represent the nonlinear system to be identified. The 'design' is then checked by applying a suite of ordinary ground motion records and compafing the multirecord incremental dynamic analysis of the peak deformation response to the target (performance) curve. The approach was found to work well for the example structures and shows promise for extension to more complicated structures and performance measures. DOI: 10.1061/(ASCE)0733-9445(2008)134:2(240) CE Database subject headings: Seismic design; Wood structures; System analysis; Identification; Frames; Probability.

The dynamic performance of a woodframe structure is examined through the qualitative correlation between the transient interstory drift and the observed damage following a series of full-scale shake-table tests. The structure was subjected to simulated Northridge earthquake ground motions scaled to seismic hazard levels of 50, 10, 2, and 1% exceedance in 50 years. Added mass was used in an effort to examine the qualitative correlation of the observed performance with the performance tabulated in FEMA 2000. The structure was repaired to the extent possible between each test. The structure was tested at three different structural/nonstructural stages: (1) oriented strand board (OSB) only; (2) gypsum wall board (GWB) and OSB; and (3) OSB, GWB, and a nonstructural interior partition wall, in order to determine the effect of each component and to qualitatively determine its effect on overall damage to the system. It was determined that qualitative damage descriptions were not significantly different from those given in FEMA 2000. It was also found that the percent torsion increased with increasing peak ground acceleration. The effect of GWB on structural response and damage was as expected, but the partition wall behaved differently than expected. Specifically, the partition wall sustained very little damage even though it had full load transfer at the top plate. DOI: 10.1061/(ASCE)0887-3828(2007)21:1(35) CE Database subject headings: Earthquake engineering; Ground motion; Performance characteristics; Shear walls; Framed structures; Wood structures; Shake table tests.

Accelerated bridge construction (ABC) has been used extensively to achieve rapid construction, to reduce traffic congestion and environmental impacts, and to ensure reliable quality control. Precast columns are typically precast with a solid section and then inserted into a socket foundation that is deeper than the maximum dimensions of the column section. To reduce the weight of the precast column and foundation for easy transportation and assembly, an alternative solution was proposed that uses a hollow section column with high-strength concrete and a foundation with a shallow socket. After the column was erected, postpour concrete (PPC) was then poured into the hollow column to a certain depth to strengthen the shear capacity in the plastic hinge region. Two precast columns with different depths of the PPC were investigated experimentally by cyclic loading test and were compared with a cast-in-place (CIP) reference column. The cyclic loading test results showed that the precast, hollow, high-strength concrete column with socket connection exhibited emulative seismic performance of the CIP reference. A deeper PPC section shows to improve the energy-dissipating capacity of the precast column. The effect of the PPC depth on the precast column and footing was investigated both experimentally and numerically. [ABSTRACT FROM AUTHOR]

In 2017, a moisture monitoring study was initiated on an eight-story, mass timber building located in Portland, Oregon. A detailed description of the monitoring program and initial monitoring results from the first year of the program were published previously. It was discovered that by the end of Year 1, some of the mass timber components had not dried below 19% moisture content (MC). This technical note is a follow-up to the original paper to examine how the building changed over its first 3 years after construction. All of the locations monitored over 3 years have reached stable moisture contents between 10% and 15%, which are acceptable for building functionality and performance. The main conclusion from this study is that mass timber buildings can naturally recover from construction wetting provided that such buildings are properly enclosed and further moisture intrusion is prevented. [ABSTRACT FROM AUTHOR]

This paper presents a new stochastic methodology for evaluating and quantifying the downtime of a structure in terms of a family of fragilities that represent the probability of exceeding prescribed times to return to functionality. This methodology integrates several existing concepts, namely, Federal Emergency Management Agency P-58 and Resilience-based Earthquake Design Initiative (REDi), to build a family of system (building) level fragility curves corresponding to the time needed to achieve different recovery levels (reoccupancy, functional recovery, and full recovery). This approach enables one to propagate uncertainty throughout the procedure so that variations in the delay time and repair schedules are accounted for in the resulting fragilities. As an illustrative example of this approach, the methodology is applied to assess the downtime of a two-story mass timber building that was originally tested at the NHERI@UCSD outdoor shake table in 2017. One unique aspect of this analysis is that it incorporates a relatively new material, cross-laminated timber (CLT), in a resilient posttension rocking wall design application. Nonstructural components representing a typical office building were selected and incorporated into the procedure for the two-story CLT rocking wall building. Time-to-functionality fragility curves are then developed for the two-story building, and potential design and resilience-focused applications are discussed. [ABSTRACT FROM AUTHOR]

Railway vehicles frequently have derailed during major earthquakes. Although a probabilistic approach based on fragility analysis was established in structural engineering, it has never been applied to railway vehicles. Thus, the aim of this study was to select optimal intensity measures (IMs) and develop fragility curves for the derailment of vehicles. Eight commonly seen IMs were examined to determine their suitability for use in analyzing the derailment of vehicles. The railway vehicle response was analyzed using a nonlinear vehicle-track simulation, and 22 far-field and 28 near-field ground motion records were used as input. Based on the results of the simulation, the correlations of these IMs with the responses of vehicles were evaluated in terms of commonly accepted criteria in the literature, such as efficiency, practicality and sufficiency. It was found that spectral IMs were superior to peak-type IMs. In addition, the acceleration spectral intensity (ASI) and the velocity spectral intensity (SI) were shown to be optimal IMs for the evaluation of derailments. Using the selected IM (ASI), derailment fragility curves were developed for three levels of vehicle performance, which facilitated the probabilistic assessment of vehicle derailment in a performance-based manner. [ABSTRACT FROM AUTHOR]

Cross-laminated timber (CLT) is a mass timber product that has recently garnered considerable attention for lateral-force resisting system (LFRS) applications. The main objectives of this study were to investigate the rocking behavior of a high-aspect-ratio (height/width) CLT shear wall without post-tensioning, and to validate a finite-element (FE) model based on the cyclic and dynamic response of the wall. To this point, high-aspect-ratio walls in the literature have primarily been post-tensioned. The testing component of this study included connector tests, quasistatic cyclic shear wall tests, and shake-table tests under four different ground motions scaled to design earthquake (DE)- and maximum considered earthquake (MCE)-level intensities. A generic shear connector was used for this study to allow for proprietary and other systems to demonstrate equivalence. The connectors were tested under shear and uplift, and shear-wall tests were performed using the Consortium of Universities for Research in Earthquake Engineering (CUREE) displacement protocol, which has been widely used for light-frame wood structures. Interstory drift (ISD) ratios in the shake-table tests ranged from 0.97% to 2.02%, and the tests demonstrated the system's ability to resist seismic loading. An FE model of the CLT wall was developed that showed good agreement with the cyclic and shake-table tests. The difference between the ISD ratios in the numerical model and the shake-table tests ranged from 5.4% to 31.3%, with an average of 17.9%, which was in good accordance with the accuracy of the existing CLT models. This system can be utilized as a retrofit option, in conjunction with light-frame wood shear walls, where lack of space may be a challenge. [ABSTRACT FROM AUTHOR]

A full-scale 2-story mass timber building was tested on the University of California San Diego Natural Hazards Engineering Research Infrastructure (UCSD-NHERI) uniaxial shake table during the period from June 2017 to September 2017. The main objective of the experimental program was to test the performance of mass timber building designs with different seismic lateral force–resisting systems. The focus of this study is on a building configuration designed using self-centering post-tensioned cross-laminated timber (CLT) rocking walls with U-shaped steel flexural plate energy dissipators. The shake-table tests were designed to subject the building to a series of earthquake ground motions of increasing intensity, ranging from a service-level earthquake to 1.20 times the maximum considered earthquake intensity. Between each ground motion, low-amplitude white-noise excitations were applied to the building, which responded as a quasilinear system. In this paper, two output-only operational modal analysis methods are used to estimate the modal parameters (frequency, damping, and mode shapes) based on acceleration data collected during the white-noise shake-table tests. The correlations of observed damage and repairs performed during the experimental program with changes in estimated modal features are reported. The modal parameters estimated from the testing program are also compared with a linear finite-element model that is used to validate the modal identification results and study the performance of the two system identification methods for CLT rocking structures. [ABSTRACT FROM AUTHOR]

This paper presents the behavior of floor diaphragms of a shake-table experiment of a full-scale 2-story mass-timber building structure. The structure consists of glued-laminated timber beams and columns, and floors and walls were designed and built making use of cross-laminated timber panels. Two different floor systems were designed, where the roof consists of a topped cross-laminated timber (CLT)-concrete composite system, and the floor level consists of untopped CLT panels connected with plywood single-surface splines. The CLT floor systems were designed to remain essentially elastic over the whole series of shake-table tests, which included testing of three lateral force–resisting systems tested at three different seismic intensity levels (service level, design basis, and maximum considered earthquake) for a total of 34 shake-table earthquake tests. Results from the testing indicate that CLT diaphragms designed to remain essentially elastic based on basic principles of structural mechanics and existing test data can achieve desired seismic performance objectives. In addition, sources of overstrength in certain elements of the diaphragm need to be explicitly considered for a holistic diaphragm design. [ABSTRACT FROM AUTHOR]

This paper presents the use of modern survey techniques, particularly light detection and ranging (LiDAR) scanning, to collect time-sensitive information before and after shake table experiments. Two full-scale, three-story residential buildings were tested simultaneously on the largest shake table in the world. The focus of this study is on the use of LiDAR to document observations during these tests. The challenges experienced during this study prompted the development of a formalized survey procedure using LiDAR scanning techniques, which can be used by other researchers when planning to collect such time-sensitive data from similar experimental programs. In this paper, damage assessment through visual inspection, which is commonly performed during full-scale tests, is compared to postexperiment assessments using postprocessed LiDAR-derived point clouds. Various examples of damage to structural and nonstructural components, including columns, bracing, partition walls, and façades, are illustrated through postshaking visual inspections as well as LiDAR-derived point clouds. The feasibility of making accurate measurements using LiDAR point clouds, and automatically detecting damage using the point-to-point cloud comparison, is presented. Finally, the relationship between observations through traditional instruments (e.g., accelerometers and laser meters) and LiDAR is discussed. In one example, the measurements from eight laser meters around the buildings are used to validate the measurements obtained using LiDAR point clouds. It is concluded that observations through LiDAR are complementary to those from traditional instruments, while permanent/residual displacements after the tests can be measured from both traditional and modern instruments. [ABSTRACT FROM AUTHOR]

Seismic force resisting systems based on cross-laminated timber (CLT) shear walls have garnered considerable attention for in mid-rise construction around the world. The purpose of this study was to determine seismic performance factors for CLT shear wall systems in platform type construction. These factors, namely, the response modification factors, R, overstrength factor, Ωo and deflection amplification factor, Cd , have been developed in this study for CLT walls and proposed for inclusion in ASCE 7. The study follows the FEMA P695 methodology that incorporates testing, evaluating a design methodology, defining the design space representative of typical construction, and comprehensive performance evaluation. The testing phase of the project consisted of connector testing and CLT shear wall testing, all with nonproprietary generic connectors to facilitate building code recognition. The design methodology and archetype development process are also discussed in this paper. A total of nine index buildings were developed from which 72 archetypes were extracted for this study. The archetypes were designed based on the design methodology and assessed with nonlinear pushover analysis and incremental dynamic analysis. Based on the required collapse margin, an R factor of 3 is proposed for CLT shear wall systems with 2∶1 or mixed aspect ratio panels up to 4∶1 , and an R factor of 4 is proposed for CLT shear wall systems made up of only 4∶1 aspect ratio panels. [ABSTRACT FROM AUTHOR]

Post-tensioned timber (Pres-Lam) buildings have been constructed throughout the world, beginning in 2010. The technology, which originated from low-damage concrete building applications, relies on unbonded post-tensioning tendons to provide moment capacity to beam–column, wall–foundation, or column–foundation connections. Supplemental energy dissipation can be introduced by the inclusion of mild steel bars or replaceable damping devices when designing buildings for high-seismic-risk areas. Given the increasing demand for multistory timber buildings in high seismic zones, the Pres-Lam system is recognized worldwide as one of many efficient solutions for achieving seismic-resilient and sustainable structures. This paper presents an overview of the current state-of-the-art of the Pres-Lam system, including experimental campaigns, numerical and analytical modeling, and operating buildings as well as design procedures and design procurement. [ABSTRACT FROM AUTHOR]

The running safety of high-speed trains over bridges is a great concern in bridge design. Typically, the running safety of vehicles is evaluated by vehicle–track simulations that are computationally expensive and unfamiliar to bridge designers. This study investigates simplified vehicle–track models for assessing the running safety of vehicles on deformed bridges. Four types of simplified vehicle models along with four types of simplified wheel–track models are investigated. The predicted wheel–rail forces are compared with those simulated by the detailed vehicle–track program. In these simulations, typical bridge deformations are taken as excitations to the dynamic system. It is found that omitting the rail vibration leads to large wheel–rail response errors. The wheel–rail constraint model gives similar wheel–rail responses to those obtained by the Hertz contact model. A vehicle–track model with five degrees-of-freedom is adequate for assessing wheel–rail forces. Furthermore, an analytical solution to the wheel–rail forces running over an angular rotation was obtained. These simplified vehicle–track models provide an efficient way to assess the running safety of vehicles on deformed bridges when using probabilistic or optimal analyses that require a large number of simulations. [ABSTRACT FROM AUTHOR]

Short span railway bridges are prone to resonate caused by dynamic train axle loads, which were usually modeled as moving point loads on the bridge in many numerical studies. In reality, the axle weight of the train is a spread load for the bridge deck because of the transfer of the track structure. Previous numerical studies indicated that the spread axle load distributed through the track structure significantly reduces bridge responses compared to the point load model. In this study, the reduction effect is investigated analytically by solving the moving load problem for both the point load and the spread load cases. The analytical solution reveals that bridge responses from the spread load model can be obtained by filtering bridge responses from the point load model. The filter function is exactly the Fourier transform (FT) of the load spreading function. Based on this relationship, a reduction coefficient reflecting the load spreading effect on bridge responses is derived. Through numerical examples, the accuracy of this proposed reduction coefficient is validated not only for the moving load models but also for vehicle-bridge interaction (VBI) problems. [ABSTRACT FROM AUTHOR]

A cross-laminated timber (CLT) panel is a heavy timber structural component fabricated by laminating layers of timber boards in an orthogonal pattern. This paper presents a study of the lateral-load response of self-centering (SC) posttensioned CLT structural walls (i.e., SC-CLT walls), which are constructed by posttensioning CLT wall panels to the foundation with vertical posttensioning steel bars. The bars pass through the CLT panels and are anchored to the CLT panels at the top of the wall and to the foundation at the bottom of the wall. Cyclic loading tests were conducted on a series of SC-CLT wall specimens with different configurations. Structural limit states of SC-CLT walls under lateral load are identified. Two types of analytical models are proposed to predict SC-CLT wall response, namely, a design-oriented analytical model based on simple mathematical expressions, and a fiber-element-based numerical model. Comparisons between the analytical and experimental results are made, which indicate that the simple mathematical expressions and the fiber-elementbased numerical model provide accurate estimates of the lateral-load response of SC-CLT walls under cyclic loading. [ABSTRACT FROM AUTHOR]

Earthquake damage to light-frame wood buildings is a major concern for North America because of the volume of this construction type. In order to estimate wood building damage using synthetic ground motions, we need to verify the ability of synthetically generated ground motions to simulate realistic damage for this structure type. Through a calibrated damage potential indicator, four different synthetic ground motion models are compared with the historically recorded ground motions at corresponding sites. We conclude that damage for sites farther from the fault (>20 km) is under-predicted on average and damage at closer sites is sometimes over-predicted. [ABSTRACT FROM PUBLISHER]

Cross-laminated timber (CLT) is a wood construction technology that has been utilized in Europe for several decades and has become even more popular recently. Although the technology has been in existence for approximately 20 years, its seismic performance has been explored only recently by a handful of researchers. Interest in bringing CLT to the North American construction market necessitates a full understanding of the seismic behavior of CLT systems and the development of a response-modification factor, known as the R-factor, for use in force-based seismic design codes. In this paper, a nonlinear, load-resistance model for CLT shear walls is developed based on reversed-cyclic test data and explained. An estimation of a possible R-factor is obtained by developing a design for a 6-story CLT apartment building, based on computed peak interstory drifts, to achieve good performance in a high seismic region of the United States. It is concluded that using the equivalent lateral force procedure with an R-factor close to 4.5 likely will provide an 80% probability of not exceeding 4% peak interstory drift during a maximum credible earthquake (MCE) near Los Angeles, CA (i.e., an earthquake with a return period of 2,500 years). [ABSTRACT FROM AUTHOR]

The understanding of, and ability to predict, the seismic behavior of woodframe structures has improved immensely in the last 10 years. Two notable projects occurred in succession, the Consortium of Universities for Research in Earthquake Engineering (CUREE) and California Institute of Technology (Caltech) CUREE-Caltech Woodframe Project, and the Network for Earthquake Engineering Simulation (NEES) NEESWood Project, which provided greater understanding, improved analytical modeling, and advances in force- and performance-based seismic design (PBSD) of woodframe buildings, respectively. The NEESWood project focused on the development of a PBSD philosophy (and procedures) for midrise woodframe buildings and included full-scale system-level validation. To date, the complete design procedure has not been systematically explained, which serves as the impetus for this paper. While the method was shown to be quite viable, some challenges remain, including identifying a format that would facilitate widespread adoption and use by engineers. Thus, this paper examines the progress, current state, and challenges for PBSD of midrise woodframe buildings. [ABSTRACT FROM AUTHOR]

Tornadoes represent a unique natural hazard because of the very low probability of occurrence, short warning times (on the order of only a few minutes), and the intense and destructive forces imposed on engineered and nonengineered buildings. The very low-probability/very high-consequence nature of a tornado strike makes designing for survival and reducing damage under typical financial constraints a substantial challenge. On April 27, 2011, an enhanced Fujita (EF) 4 (EF4) tornado devastated an almost 10-km (5.9-mi) long, 0.8-km-wide (1/2-mi-wide) path, through the city of Tuscaloosa, Alabama, and continued on the ground for 130 km (80 mi). This paper presents the design concept that resulted following a week-long data reconnaissance deployment throughout the city of Tuscaloosa by the authors. The dual-objective philosophy proposed herein is intended to focus on both building damage and loss reduction in low-to-moderate tornado wind speeds and building occupant life safety in more damaging wind-speed events such as EF4 and EF5 tornadoes. The philosophy articulates a design methodology that is the basis upon which structural engineering was formed-namely, provide life safety and control damage-but the new philosophy is focused at separate tornado intensity levels. [ABSTRACT FROM AUTHOR]

A total of 1,625 tornadoes occurred in the United States in 2011, resulting in economic losses that exceeded $25 billion. Two tornado outbreaks stand out because they caused more than half of those losses. The tornadoes that cut through Tuscaloosa, Alabama, on April 27 and Joplin, Missouri, on May 22 were responsible for a combined 223 fatalities and more than 13,000 damaged buildings in the two cities. Although the economic losses associated with tornado damage are well documented, the writers argue that the overall impact should encompass longer term, broader considerations such as the social disruption and psychological effects that impact communities. This paper examines observations by tornado damage assessment teams led by the first author in these two medium-sized cities and suggests that the evolution of building codes and past approaches to construction have led to conditions that made this extent of damage possible. The authors outline a multidisciplinary path forward that incorporates engineering research and social and economic studies into a new design paradigm leading to building code changes and social practices that will improve resistance and mitigate future losses at a community level from tornadoes. [ABSTRACT FROM AUTHOR]