AbstractA strong mainshock may cause several aftershocks within a short interval. These aftershocks can make buildings damaged during the mainshock more vulnerable to collapse. Hence, it is critical ...to study the seismic responses of a structure during aftershock events following a major shock. The focus of this work was to investigate the seismic fragility of an emerging high-performance seismic-resistant system—the self-centering energy-absorbing dual rocking core (SEDRC) system—considering mainshock–aftershock sequences, and to compare SEDRC with traditional systems. First, three- and six-story SEDRC systems were designed following the direct displacement-based design method to show comparable maximum interstory drifts compared with those of the three- and six-story benchmark buckling-restrained braced frames (BRBFs), respectively, under the design-basis earthquake excitations. Second, 30 as-recorded mainshock–aftershock sequences were selected. The dynamic analyses and incremental dynamic analyses (IDAs) were conducted to study the seismic responses of the four buildings with the mainshock inputs alone and the mainshock–aftershock sequence inputs. The analysis results show that the designed SEDRC systems and BRBFs can obtain comparable performance in limiting the maximum interstory drifts (MID) responses, whereas the SEDRC systems are more efficient in limiting the maximum residual interstory drifts (MRD). Moreover, the SEDRC systems perform much better than BRBFs in resisting structural collapse. As expected, the aftershocks would increase the MID, but may increase or decrease the MRD of the SEDRC systems and BRBFs. Finally, the seismic fragilities of the designed systems were further investigated on the basis of the results from the IDAs in a probabilistic framework using a joint probability density function with the consideration of both MID and MRD. The advantages of the SEDRC systems in achieving excellent seismic collapse-resistant and self-centering capacity were explored through probabilistic analyses.
•Prediction models of Cμ and Cr were developed for the RSMRF.•A peak and residual displacement-based design method was developed for retrofitting SMRFs.•The designed RSMRFs can achieve the desired ...peak and residual inter-story drift responses.•The designed RSMRFs have no repair requirements for after MCE excitations.
Conventional steel moment-resisting frames (SMRFs) absorb seismic energy through steel yielding behavior, leading to significant residual displacement. Although steel yielding behavior can ensure the seismic safety of SMRFs under strong earthquakes, excessive residual displacement may lead to post-earthquake demolition decisions, causing a large amount of economic loss. This paper aims to develop a peak and residual displacement-based design (PRDBD) method for controlling the peak and residual inter-story drift responses of SMRFs by installing self-centering braces. The peak and residual displacements are both set as the design targets in the proposed PRDBD method. To this end, the machine learning prediction models of inelastic and residual displacement ratios were first developed based on the median responses of single-degree-of-freedom systems under earthquakes. The detailed design steps of the proposed PRDBD method were subsequently introduced. The three- and nine-story demonstration buildings were retrofitted by using the PRDBD method with two different design targets. Static and dynamic analyses were conducted to validate the effectiveness of the proposed PRDBD method. The static analysis results indicated that the self-centering braces could efficiently enhance the SMRF’s stiffness and strength. The retrofitted SMRFs showed no strength deterioration, whereas the original SMRFs showed obvious strength deterioration at the roof drifts of 3.2% and 2.5% in the three- and nine-story buildings, respectively. The dynamic analysis results confirm that the self-centering braces can efficiently reduce the peak and residual inter-story drift responses of the existing SMRFs and the retrofitted SMRFs can achieve the peak and residual inter-story performance objectives under the considered seismic intensity. Moreover, the retrofitted SMRFs can be fully recoverable after maximum considered earthquakes by controlling the maximum residual inter-story drift lower than 0.2%.
•A coupled reinforcement consisting of SMA and steel rebars is proposed for RC bridge piers.•An optimal design of the coupled reinforcement ensures balance between energy dissipation and ...self-centering.•The probabilistic seismic fragilities and life-cycle losses of the bridge with different reinforcements are investigated.•The probability of earthquake damages of the bridge can be reduced by introducing SMA rebars.•The coupled reinforcement minimizes the seismic losses of the bridge in a life-cycle context.
Concrete bridge piers with conventional steel reinforcing bars are vulnerable to strong earthquakes by inducing significant residual deformations, which substantially weakens the seismic resilience of bridges. Superelastic shape memory alloy (SMA) bars showing superior self-centering capacities are desirable substitutes to steel reinforcements to minimize the seismically-induced residual deformations of piers. Nevertheless, high cost, difficult machining, and lack of sufficient energy dissipation are the primary restraining factors to a wide implementation of SMA reinforcements. This study proposes a novel SMA-steel coupled reinforcement for concrete bridge piers, which is intended to achieve the balance between self-centering and energy dissipation capacities. Probabilistic seismic fragility analyses are conducted on the prototype bridge with either pure steel, SMA-steel coupled, or pure SMA reinforcements to evaluate their probability of damage at different limit states. Seismic loss analyses are further performed to compare the relative cost-effectiveness of different patterns of reinforcements. The results indicate that an optimal amount ratio between SMA and steel bars can be found for the coupled reinforcements, which shows lower vulnerabilities and higher resilience under earthquakes than the other reinforcement patterns. The direct repair loss and the indirect downtime loss after earthquakes are considerably reduced when the SMA reinforcing bars are introduced. The coupled reinforcement with the optimal SMA-steel amount ratio shows the most effectiveness in mitigating the long-term economic impacts induced by seismic hazards within the lifetime of the bridge.
•Experimental test of a novel bracing system equipped with SMA bars is presented.•Seismic performance of a building equipped with such bracing system is evaluated.•The Closed-Loop Dynamic testing ...method is proposed to perform seismic test.•Very good agreement between the simulation and the experimental results was achieved.•The performance of the system under strain rate effect showed very good response.•A building with such bracing showed self-centering behavior under seismic load.
This study investigates the seismic performance of a newly developed self-centering bracing system using a novel experimental technique named as closed-loop dynamic (CLD) testing. The bracing, named piston-based self-centering (PBSC) apparatus, employs Ni-Ti superelastic shape memory alloy (SMA) bars inside a sleeve-piston assembly for its self-centering mechanism. During cyclic tension-compression loading, the SMA bars are only subjected to tension avoiding buckling and leading to flag-shaped symmetric force-deformation hysteresis. Initially, a braced frame building fitted with PBSC is seismically designed and the preliminary sizing of the brace is determined. For testing, considering the lab capability, the brace is fabricated at a reduced scale. The process of “Closed-loop dynamic testing” starts with the brace test (step 1) under strain-rate loading to characterize the numerical model parameters (step 2), which are then scaled-up as per similitude law and implemented in a finite element software, S-FRAME’s PBSC brace model (step 3). Then the braced frame building is analyzed under an earthquake (step 4) and the axial force-deformation response of the brace under consideration is captured (step 5). In order to further understand and validate the actual response of the brace under earthquake type loading, the axial deformation obtained from S-FRAME is scaled-down (step 6) and used as input parameters for testing the reduced scale brace (step 7). The obtained response (step 8) is further scaled-up and used to match the S-FRAME’s PBSC model for validation (step 9). Iterations from step 3 to step 9 will be required until the experimental and numerical results converge. Convergence criteria used for this validation include both the energy dissipation capacity and initial stiffness within 10% accuracy. Reasonable agreement between the numerical and experimental results is achieved in the closed-loop dynamic testing. The PBSC brace shows excellent self-centering capability under various earthquake loadings.
•A SCENARIO system consisting of an RC and two FSDs was tested.•The SCENARIO specimen exhibits self-centering behavior under large lateral drift.•The finite element model of the SCENARIO specimen was ...introduced and verified.•The influences of non-uniform compression of friction springs in FSDs were studied.•A performance-based design method was proposed and validated for SCNEARIO systems.
The Self-Centering Energy-Absorbing Rocking Core with friction spring damper (denoted as the SCENARIO system) is a novel steel structural system that can achieve excellent self-centering performance in low-rise buildings. This research presents the physical tests and design procedure of the SCENARIO system, which consists of a rocking core (RC) and two friction spring dampers (FSDs). The basic mechanical response of the friction ring spring group included in the FSD is first described through a preliminary experimental study. Three repeated rounds of reverse cyclic load tests of the SCENARIO system are conducted. The test results show reliable and stable self-centering hysteretic behavior. After removing the applied force at the maximum loading roof drift ratio of 5%, the SCENARIO specimen achieved near-zero residual drift. During the entire loading process, the RC can remain elastic. The two FSDs included in the SCENARIO specimen show yield force reduction and stiffness increase under three repeated rounds of cyclic loading. However, there was no damage to any components in the FSD after the tests. Following the experimental study, the finite element model of the SCENARIO system is introduced and verified. Then, nonlinear dynamic analyses (NDA) are performed to determine the influences of the yield force reduction and stiffness increase of the FSD on the seismic performance of the proposed system. Finally, a performance-based design procedure is proposed using the direct displacement design method for the SCENARIO system. The results from the NDA indicate that the SCENARIO system designed via the proposed design procedure can achieve the desired performance objective and excellent self-centering behavior under the maximum considered earthquakes.
AbstractCross-laminated timber (CLT) has been gaining popularity also in seismic regions, because of its low carbon footprint and potential cost-competitiveness with concrete and steel construction. ...Recent effort has focused on developing standardized design provisions for CLT buildings. In the study presented herein, incremental dynamic analysis (IDA) was performed on a six-story CLT platform-type building. A nonlinear numerical model was developed in OpenSees considering the CLT shear walls as elastic shell elements and the connections (wall-to-foundation, wall-to-floor, and wall-to-wall) as nonlinear springs. The hysteresis behavior of the connections was modeled using “pinching4” after calibrating its parameters against experimental results, and the load-deformation response of the shear walls was validated against full-scale test results. The building’s seismic performance—terms of interstory drift until collapse—was evaluated using fragility curves constructed from the IDA. The probability of collapse was less than 0.1% at the maximum considered earthquake, and the resulting collapse margin ratio demonstrated that a six-story CLT platform-type building can safely be built in a high seismic zone if appropriately designed.
In recent decades, a variety of self‐centering braces (SCBs) have been developed to address the limitations of conventional frames by decreasing residual drift due to earthquakes. However, the ...initial construction cost of self‐centering (SC) structures is expected to be higher and the study about its cost‐effectiveness over the life‐cycle span is limited. This paper presents a seismic life‐cycle cost evaluation of emerging friction spring‐based self‐centering braced frames (SCB‐Fs) compared with traditional buckling restrained braced frames (BRB‐Fs) when an existing structure is upgraded. Particular focus is on the effect of residual deformation, initial construction cost, and high fatigue performance of the SCB. Following the performance‐based design of the SCB‐F and BRB‐F, system‐level analyses are conducted. Numerical results of case‐study buildings indicate that the total expected annual loss (EAL) of the BRB‐F increases by approximately three times when the effect of residual deformation is considered, while its effect on the total EAL of the SCB‐F is negligible. Besides, the superior performance of the SCB‐F compared to BRB‐F is highlighted by a substantial reduction in EAL induced by earthquakes. In addition, the acceleration‐related seismic losses of SCB‐F constitute approximately 44% of the total EAL. Its contribution is significantly larger in the case of the SCB‐F compared to the BRB‐F. From the perspective of economic benefit, increasing the structural life‐cycle span is beneficial to the SCB‐F compared to the BRB‐F. The high fatigue performance of the SCB is favorable to increase the economic benefit of the SCB‐F, especially when the reduction of repair time is considered. The economic benefit of the SCB‐F compared to the BRB‐F is highly related to the initial construction cost. Taking the 100 years as an expected life‐cycle span, the high initial construction cost of the SCB‐F would not be paid off when the unit cost of the SCB is about 2.1 times that of the BRB.
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•A novel aseismic system – hybrid self-centering rocking core system - was proposed.•A performance-based design method is developed for the HSRC system.•The HSRC systems show ...excellent performance in controlling structural damage and have enough redundancy to resist building collapse under extreme earthquakes.•The HSRC systems can show excellent recoverability against extreme earthquakes.•The HSRC systems can show credible performance in controlling nonstructural damage.
This research presents a novel aseismic system, the hybrid self-centering rocking core (HSRC) system, for obtaining better seismic resilience in steel buildings. Two hybrid self-centering dampers are introduced in the HSRC system to control structural and nonstructural damage. A rocking core, i.e., a steel braced frame with pinned base is included in the HSRC system to facilitate uniform inter-story drift responses under earthquakes. The steel braces in the rocking core can also work as a reserve energy-absorbing mechanism against structural collapse subjected to extreme seismic events whose intensities are more significant than those of the maximum considered earthquakes in design codes. The desired nonlinear responses of the HSRC system were analyzed. Direct displacement-based design steps were developed for the HSRC system. Three-story and six-story HSRC systems were designed following the proposed design method. Nonlinear dynamic analysis results indicate that the designed HSRC systems can show desired nonlinear responses and achieve the expected performance objective under earthquakes. Moreover, seismic fragility analyses were also conducted based on the incremental dynamic analysis results to assess the performance in controlling structural and nonstructural damages of the HSRC system under earthquakes of different intensities. The results confirm that the proposed HSRC system has excellent capacity in resisting structural collapse, achieving reliable post-earthquake recoverability, and controlling structural and nonstructural damage under rare seismic events.
AbstractThe influence of recycled coarse aggregates (RCAs) on the fresh, hardened, and freeze-thaw durability properties of recycled aggregate concrete (RAC) is investigated in the research reported ...in this paper. Four different mixes were considered with natural aggregate and three different replacement levels of RCA i.e., (1) 30%, (2) 40%, and (3) 50%. The fresh and hardened properties of RAC were investigated according to national standards where the target strength was 35 MPa in 56 days. The compressive strengths of different concrete mixes were determined after 3, 7, 28, 56, and 120 days of moist curing. The results are also presented in terms of stress-strain curves, modulus of elasticity, and Poisson’s ratio. Freeze-thaw durability performance of RAC was studied in accordance with a national standard. This paper shows that the performance of RAC slightly decreases with increasing RCA replacement levels; however, their overall performance is comparable to natural aggregate concrete (NAC). This paper indicates that the use of RCA in new concrete production can lead to a greener environment and pave the way for sustainable construction.
Implementing energy dissipation braces can be an effective option for mitigating the seismic damage of double- or multi-column bridge bents. This study compares the relative effectiveness of ...different braces in seismically retrofitting a reinforced concrete (RC) double-column bent. The considered braces include buckling-restrained braces (BRBs), viscous damper braces (VDBs) and piston-based self-centering braces (PBSCs). First, a direct displacement-based design method (DBD) is utilized to design the braces for satisfying the same performance criterion under design earthquakes. Based on that, fragility analysis is conducted to evaluate the seismic vulnerability of the retrofitted bents subjected to near-fault and far-field ground motions. The self-centering performance of the retrofitted bents is also compared by using the post-earthquake residual displacement as a performance indicator. Results indicate that the PBSCs are more effective than BRBs and VDs in reducing the vulnerability of the bent at different damage states under either near-fault or far-field ground motions. In addition, the PBSCs are superior to the other braces in terms of self-centering performance by recovering more bent drift from an earthquake.
