Journal of Structural Engineering

ACI 318-19 and ASCE 7-22 specify code-compliant and emulative seismic force-resisting systems (SFRS) including intermediate precast shear wall systems. For the seismic design of a precast shear wall system, its successful performance heavily depends on the capacity design of inevitable discrete connections between precast wall panels, thus playing a critical role in controlling yielding to occur within steel reinforcements at the vicinity of intended locations or components. This is imperative for achieving not only ductility but also adequate energy dissipation, ensuring the system can effectively withstand seismic forces. To this end, the overstrength is essentially required to prevent any brittle failure, and the connections designed not to yield can be protected by addressing the $1.5S_y$ condition as specified in ACI 318-19 and ASCE 7-22. However, there can be a blind spot for the precast connections designed to yield. To this end, this study showed some cases based on practical examples from which a reasonable magnitude of overstrength ($S_y$) was tentatively recommended for better safety in the seismic design of the intermediate precast shear wall system with precast connections designed to be yielded.

To improve shear capacity, as well as reduce on-site casting and steel consumption, a novel Y-shaped perfobond rib (Y-PBL) shear connector with ultra-high-performance concrete (UHPC) grout was proposed. The shear behavior of the Y-PBL shear connector was investigated by six groups of pushout specimens. Their failure modes, load–slip curves, load–separation curves, strain analysis, and shear transfer mechanisms were discussed. Subsequently, finite-element analysis (FEA) models were established to study the effect of parameters on the shear behavior of the Y-PBL shear connector, as well as to compare the shear capacity contributions with straight-shaped PBL (S-PBL) shear connectors. Analytical models were proposed to predict the shear capacity of the Y-PBL shear connector. The results reveal that the proposed Y-PBL shear connector has superior shear capacity and stiffness. The contribution of the perforating rebar is minor compared with the end-bearing effect of UHPC. The analytical predictions agree well with the experimental and FEA results. This study can be used to guide the design and application of the Y-PBL shear connector in steel-concrete composite bridges.

The state of Hawaii is a series of mountainous islands with a topography that is much more complex than the simple isolated hills and escarpments included in ASCE standard ASCE/SEI 7-22 (Minimum design loads and associated criteria for buildings and other structures, ASCE 7). Hawaii state and county building codes have incorporated topographic wind speed mapping since 2007. In 2010, ASCE 7-10 recognized Hawaii as a special wind region. The design wind speed maps, $K_{zt}$ maps, and site-specific directionality factors as adopted in Hawaii’s state building codes constituted the “special $K_{zt}$ topographic effect adjustments” of the authority having jurisdiction that were referenced in ASCE 7-10. In ASCE 7-16 and ASCE 7-22, microzoned wind speed maps for Hawaii, including the effect of topography and directionality, were incorporated for strength design return periods. This paper provides information on the development of an improved generation of higher-resolution basic design wind speed maps for the state of Hawaii, including better accuracy of topographic and directionality effects. The digital format of these wind speed maps can be readily incorporated into the ASCE 7 digital hazard tool interfaces.

Two methods to predict the pushover response of a hybrid steel braced frame that features concentric and eccentric connections are presented. The proposed hybrid frame configuration is intended for cold-formed steel (CFS) building structures and plays a dual role by providing gravity and lateral load resistance. The hybrid system features CFS columns for resisting gravity loads, tension only CFS straps connected concentrically to hollow structural steel (HSS) chords for resisting lateral loads, and prestressing strands connected eccentrically to the same HSS chords for further enhancing lateral load capacity. The first pushover response prediction method employs a nonlinear finite element modeling protocol that features only beam and truss elements. This method is presented as an alternative to three-dimensional (3D) nonlinear finite element models, which require considerable modeling effort due to the multitude of the components included in the hybrid system, and the variety of interactions that would need to be defined. The second method includes closed form equations that allow the definition of the pushover curves using manual calculations and is appropriate for preliminary analysis. Formulations for predicting the initial in-plane system stiffness, and secondary stiffness are presented. Similarly, formulations for predicting the load to cause the first and second yield as well as ultimate lateral load capacity are provided. A closed form equation is presented to obtain the ultimate lateral displacement, which completes the definition of the pushover curve. The validation of the proposed pushover response prediction methods is conducted by first comparing responses from 3D nonlinear FEA to those obtained from the simplified FEA model. Similarly, predictions from the simplified FEA model are compared to those obtained from the closed form equations. Good agreements are noted in both cases. The influence of hybrid steel braced frame aspect ratio on system push over response is quantified. The contribution of each lateral load resisting element to lateral load capacity is presented as a function of aspect ratio. Finally, improvements in behavior and enhancements in lateral load capacity offered by the hybrid frame-wall compared to the traditional strapped wall system are demonstrated through monotonic pushover, cyclic pushover, and response history analysis.

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.

The building industry requires the development of a ductile lateral force resisting system made of mass timber to help mass timber to continue to grow in popularity as the primary structural building material. The OpenSees framework was used to develop a numerical model of a single-story timber frame with a timber buckling-restrained brace, which was validated by the results of a previously completed series of quasistatic cyclic timber buckling-restrained brace (TBRB) component and subassembly tests. The experimental validation included a model developed for the hysteretic behavior of the TBRB and the rotational capacity of beam–column joints made with mass ply lam (MPL) panels, two slotted-in steel plates, and a number of steel dowels. The single-story model TBRB braced frame was then expanded to a numerical model of an eight-story mass timber buckling-restrained braced frame. The TBRB frame was analyzed with static pushover, quasistatic cyclic loads, and earthquake simulations. During the simulation of eleven design-level earthquake ground motions, the building experienced a peak interstory drift at of 2.54% at the first-floor level and a peak floor acceleration of 1.7g at the roof. The numerical model developed in this research of a timber buckling-restrained braced frame with TBRBs is novel and could be used to design timber buckling-restrained braced frames as a ductile lateral force resisting solution for mass timber buildings in seismic regions.

In this paper, an innovative hamburger-shaped eddy current damper (HSECD) is presented to mitigate the responses of civil structures subjected to wind excitations. The damper’s capacity to dissipate energy is significantly enhanced through a two-phase configuration of permanent magnets (PMs) and two transmission devices: a ball-screw assembly and a bevel gear group. The improved eddy current damper (ECD) solves the problem that the low damping density of traditional ECDs hinders their application to the field of vibration control for civil structures. First, the construction details of this novel HSECD are elaborated, and its principle is discussed through theoretical analysis and numerical simulation. Subsequently, a prototype of the HSECD was fabricated, and cyclic tensile–compressive tests were conducted to investigate its mechanical performance. Furthermore, the temperature effect on the damper’s maximum output force was analyzed, and more than 10% performance degradation was detected in tests with a continuous loading of 1,250 s, while the damper performance quickly reached a steady state after a certain decline. A theoretical model of the HSECD was then established to simulate its hysteretic characteristics, and the accuracy was verified by comparing it with the test data, where their energy error was only 1.9%. Finally, the application of the HSECD to both a single-degree-of-freedom (SDOF) simplified system and a jacking engineering system demonstrates its excellent control performance because the reduction ratios of their peak displacement were as high as 31.1% and 40.9%, respectively. These results highlight the significant practical value of the HSECD in mitigating the wind-induced vibrations for engineering structures.

Backbone curves were generated from previous physical lab tests conducted on identical full-scale RC components utilizing different loading protocols (slab–beam–column and column specimens). These curves were subsequently compared with those prescribed in ASCE 41. It was observed that there was a substantial difference between the two, with ASCE 41 backbones (based on standard tests) showing significantly lower ductility capacity compared to backbones from tests using a loading pattern representative of earthquake demands, leading to a near-collapse condition. A four-story archetype RC building was analyzed to assess the influence of different backbones on its seismic response. The analysis revealed that using backbones representative of earthquake demands produced a median spectral capacity somewhere from 25% to 50% greater than that obtained using ASCE 41 upper bound backbones. Similarly, for drift capacities at incipient collapse, it was found that using backbones representative of earthquake demands resulted in a median capacity somewhere between 1.6 and 2.9 times that of using ASCE 41 upper bound backbones. These differences are significant, implying that ASCE 41 can be overly conservative by rejecting buildings that would otherwise be acceptable if ASCE 41 criteria were based on tests using protocols representative of earthquake demands. Examination of the time-history responses of the study building revealed that earthquake demands were predominantly characterized by relatively few large drift excursions having a one-direction bias. Standard protocols differ significantly from responses observed during actual earthquakes, as they feature numerous symmetrical fully reversed cycles of drifts with progressively increasing amplitudes that are much more demanding. This leads to overly conservative ASCE 41 criteria (too pessimistic). It is concluded that future component lab tests must include protocols representative of earthquake demands to achieve more accurate estimates of component behaviors. Use of such protocols will lead to more appropriate (less conservative) ASCE 41 building evaluations, aligning more consistently with the philosophy of performance-based earthquake engineering.

A fragility-based probabilistic framework is proposed for the optimal design of friction pendulum (FP) bearings in seismically isolated liquid-storage tanks. The isolation period and sliding friction coefficient of the FP system, which significantly influence the seismic performance of isolated liquid-storage tanks, were analyzed as the two design parameters of the isolation system. The seismic fragility functions of the isolated tanks, generated using incremental dynamic analysis (IDA), were evaluated and used to determine the optimal ranges for these design parameters. This procedure, which yields the minimum seismic failure probability of the considered structures, was examined in the design of seismic isolation systems for two on-grade cylindrical steel storage tanks with broad and slender configurations. Moreover, the effects of including or excluding the failure mode corresponding to the excessive displacement of the isolation system from the considered failure limit states were analyzed and discussed. Finally, the present study provides recommendations for the optimal selection of design parameters for FP isolators in liquid-storage tanks.