Hysteretic Energy Dissipation Research Articles

Dual Physically Crosslinked Silk Fibroin Ionoelastomer with Ultrahigh Stretchability and Low Hysteresis

Innovations in ionotronics have greatly facilitated the development of ultraflexible devices, displays, and machines. However, ionotronics often suffer from an inherent trade-off between stretchability and elasticity due to their viscous nature. Here, we overcome this limitation by incorporating dimension-and-content-confined nanocrystalline crosslinks into amorphous and molecularly entangled silk fibroin (SF) ionotronics. The welding-entanglement network exhibited a 34-fold increase in Young’s modulus, a 14-fold increase in tensile strength, and a 9-fold increase in toughness compared to the same SF material without the nanocrystal crosslinks. The welding-entanglement network also gained recoverable hysteretic energy dissipation with hysteresis as low as 22%. The stretchability and low hysteresis exhibited by these SF ionoelastomers far exceed those of previously reported ionotronics and bioelastomers. These mechanical merits, together with the inherent advantages of SF ionoelastomers, including their multiprocessability, sustainability, biocompatibility, and degradability, promote their applications in human–machine interfaces and bio-functional devices.

Seismic damage model for gypsum board-to-CFS stud screw connections considering ground motion duration

First, a cyclic loading method of gypsum board-to-cold-formed steel (CFS) stud screw connections was explored, and the impact of ground motion duration was considered. Then, the correlation between the shear behavior of the screw connections and ground motion duration was investigated. Afterward, a screw-sheathing abrasion theory was proposed, and the shear performance degradation mechanism of the screw connections was further revealed. Moreover, a method for determining the load-deformation relationship of the screw connections was established. Ultimately, a seismic damage model for gypsum board-to-CFS stud screw connections considering the impact of ground motion duration was established based on an improvement of the Park-Ang seismic damage model. The results are as follows: (1) The load-deformation curves of the screw connections show nonlinear characteristics accompanied by strength and stiffness degradation and pinching. The primary control of the load-deformation curves and shear damage of the screw connections is extrusion of the screw from the gypsum board. (2) The shear damage of the screw connections is positively correlated with the number of loading cycles originating from long-duration ground motions. (3) A load-deformation relationship of gypsum board-to-CFS stud screw connections considering the influence of the loading path can be established accurately through the proposed screw-sheathing abrasion theory. (4) The proposed seismic damage model reflects the change in the ultimate energy dissipation capacity of gypsum board-to-CFS stud screw connections with a hysteretic energy dissipation process. The damage development of the screw connections can be accurately described, indicating good applicability to sheathing-to-CFS stud screw connections dominated by sheathing bearing failure.

Seismic performance of concrete-filled steel tubular composite columns with ultra high performance concrete plates

Two 1:8 scale specimens were designed and created to examine the seismic performance of concrete-filled steel tubular (CFST) composite columns with ultra high performance concrete (UHPC) plates. Ground motion characteristics, axial pressure ratio, plate material, and mainshock-aftershock sequences were used as parameters in the pseudo-dynamic test study. The results show that the ground motion characteristics have a significant effect on the seismic response of the specimen; The initial stiffness of the specimens is mostly unaffected by the axial pressure ratio. Furthermore, the larger the axial pressure ratio, the earlier the specimen enters yielding and the more severe the final failure phenomenon; After UHPC was used in place of the plate material, the specimen's initial stiffness rose by about 13.7%, the stiffness degradation of the specimen was somewhat delayed, and the hysteretic energy dissipation increased by about 41.2%.; The specimen undergoes elastic, elastoplastic, and plastic failure stages under the aftershocks of increasing intensity. Under the mainshock-aftershock sequences of the same intensity, the seismic response of the specimens under the aftershock was not much different compared to the mainshock, and the hysteretic energy dissipation was about 67.7% and 74.5% of the mainshock respectively. These structures can withstand multiple earthquakes and have demonstrated good seismic performance.

Comparing crack density and dissipated energy as measures for off-axis damage in composite laminates

To investigate off-axis cracks in composite laminates and their effect on stiffness and hysteretic energy dissipation, fatigue tests were instrumented with automated crack detection to test damage onset and progression. It was found that the onset of stiffness loss correlates well with the onset of matrix cracks, but not with the dissipated energy. To study the transition between experimentally observed damage modes occurring at the micro-scale, the experimentally obtained dissipated energy was compared with Carraro’s model, which predicts this transition based on local stresses. The results show a correlation between the absolute level of dissipated energy and the micro-damage modes.

Experimental and numerical investigations of bolted assembled joints to concrete encased CFST columns with different connection details

Concrete encased CFST (CECFST) composite components have prominent advantages over traditional CFST components such as better durability, high stiffness and strength, etc. However, the encased concrete outside caused certain difficulty in connecting to the steel beam. In this paper, two types of bolted assembled joints between CECFST column and steel beam were proposed and tested under cyclic loads, in which the end plate and cover plate joints were included. Typical failure modes of the joints were analyzed and characterized. In comparison, the CECFST column in end plate joints exhibited more severe failure and higher strength than that in cover plate joints. Seismic performance including hysteretic curves and energy dissipation were also discussed. In addition, numerical modelling of the joint was established considering the complicated material models and interactions in the joint core, of which the accuracy was validated against the test results. Further, parametric analyses were performed on the cover plate joints with CECFST columns through the numerical approach. It demonstrated that the axial ratio, thickness and strength of cover plate, diameter of bolt, strength and thickness of steel tube significantly affected the stiffness and strength of the joint. The experimental and numerical results revealed that the proposed two types of joints with CECFST column performed relatively favorable seismic behavior and could be employed in engineering practice.

Catechol-modified epoxy backbones for multifunctional and ultra-tough thermoset

Widely used traditional thermosets have drawn great attention due to their advantageous features such as excellent stability, mechanical reliability etc. However, brittleness is still the weak point in their extensive applications. Herein, a synthetic strategy to incorporate catechol groups into polymer structures via thiol-epoxy click chemistry was developed, the covalent and iron-catechol coordination bonds are combined to build up the material consisting of two types of crosslinks. As an important design feature of thermoset, catechol moiety provided the potential of gaining recoverable hysteretic energy dissipation through iron-catechol complexes. Favorable thermal properties comparable to commercial resin were retained, and mechanical testing revealed the thermoset exhibited high extensibility, such that it can be stretched to over 100 % with a fracture strength of 31.16 MPa, along with the tensile strength can be maintained 90.53 % after 5 cycles at the strain of 50 %. The synergistic interaction additionally providing the possibility of shape memory response to specific environmental changes, either by heat or by ultraviolet light. These behaviors further highlight the utility of dynamic coordinate bonds in the preparation of versatile thermosets, which could be potentially applied in smart devices and advanced materials.

Behaviour of double-corrugated steel plates under cyclic in-plane shear loading: An experimental study

Double-corrugated plate shear wall (DCPSW) is a new member developed based on the single-corrugated plate shear wall (CPSW). Due to its improved stability and shear resistance, it has good application potential in buildings subjected to large shear loads. Up to now, the reported experimental data of DCPSWs under cyclic loading are limited and the shear behaviour of double-corrugated steel plates in DCPSWs is needed to be further understood. This paper presents an experimental study on the double-corrugated steel plate under cyclic in-plane shear loading. Ten specimens were tested and the varied parameters included the height of corrugation, the width of subpanels in corrugation, the spacing of connecting bolts and the number of bolt columns at each valley region. The experimental results in terms of failure modes, load versus deformation hysteretic curves, skeleton curves, energy dissipation and stiffness degradation were discussed. By analysing the effects of important parameters, the mechanism of the double-corrugated steel plate under pure shear loads was revealed. It is found that the specimens failed with shear buckling which behaved as either global buckling or local buckling. Due to the combination effect, the shear resistance of the double-corrugated plate was higher than that of the single-corrugated plate with the same steel volume. Increasing the corrugation height is beneficial to improving the shear buckling load and maintaining the energy dissipation capacity. It is suggested that the ratio of corrugation height to thickness is higher than 15 in the design of the double-corrugated plate.

Seismic performance of column-bearing silo structure with granular materials considering SSI effect

This paper investigates the effects of different silo height-to-diameter ratios, different storage categories and different site soil categories on the seismic performance of column-bearing concrete grain vertical silo structures considering soil-structure dynamic interaction (SSI). The study reveals more comprehensive response mechanism of soil-pile-silo structure with grain storage system under earthquake actions. The numerical results indicate that for the full silo models with different height-diameter ratios, the SSI effect could reduce the absolute acceleration response, and the reducing rate at the top of the support column will be slightly larger than that of the top of the silo. In addition, the greater the height-diameter ratio, the more obvious the absolute acceleration damping effect of the SSI effect. The SSI effect has the greatest damping effect on the absolute acceleration response when the silo is filled with wheat. Moreover, the degree of softness and hardness of the soil affects the shock absorption effect of SSI on the absolute acceleration and elastic–plastic acceleration of the silo. The softer the soil, the more obvious the shock absorption effect of SSI. More interestingly, among the parameters of height-diameter ratio, storage material type and dynamic shear modulus of soil, the height-diameter ratio has the greatest influence on the seismic response and hysteretic energy dissipation performance of the column-bearing silo structure considering SSI effect, followed by the foundation soil. Dynamic shear modulus and the storage material category have the least influence.

Wind-Induced Impact Behavior of Base-Isolated High-Rise Buildings with Adjacent Structures

The base-isolation technology has been increasingly applied in high-rise buildings in recent years. Previous studies have shown that the unfavorable wind-induced response can be effectively reduced by a certain degree of hysteretic energy dissipation after the yielding of the isolation system under strong wind load. However, a large relative inelastic displacement at the isolation level will occur under this condition, which is likely to exceed the width of seismic gap, and cause a structural impact with the adjacent structures (i.e. retaining wall or other barriers). Such wind-induced impacts may have detrimental consequences on the structural performance and have not been investigated much before. This study prospectively investigated the wind-induced impact behavior of base-isolated high-rise buildings with adjacent structures. The multi-story superstructure is modeled as a linear elastic shear building, while the isolation system is represented by bilinear hysteresis restoring force model. An impact element combined with linear spring and damper is used. The story wind load is determined by its cross power spectral density (PSD). Responses for two kinds of typical impact including crosswind and along-wind impact are examined by time history analysis. The results demonstrate that the impact will increase the fluctuation components of superstructure displacement, shear force and bending moment to some extent compared with that of the base-isolated building without impact. The floor accelerations, especially floors close to the base, are significantly increased during impact. The impact has no effect on the mean component of each response. At last, a parametric analysis is carried out to explore the influences of various impact parameters on the inelastic impact response. The results of this study can help to better understand the impact behavior of base-isolated high-rise buildings under strong wind excitation and be useful for performance-based wind resistance design.

Resilient seismic design of reinforced concrete framed buildings with metallic fuses including soil-structure interaction effects

In this paper, the authors propose and validate a code-oriented, resilient design methodology for reinforced concrete buildings with intermediate moment frames (RC-IMFs) and hysteretic energy dissipation devices (HEDDs) mounted in chevron steel bracing design as structural fuses, considering soil-structure effects. The design methodology is based on global lateral stiffness balances among different structural components (frames, bracings and HEDDs). Global seismic design parameters were specifically assessed for such stiffness ratios through extensive parametric studies for the subject structural system under study. In order to achieve an immediate occupancy seismic performance, the design sequence using capacity-design principles is clearly established and emphasized for the design of main structural elements. Soil-structure interaction (SSI) effects are included in the formal design process following the recommendations available in the seismic code for Mexico City. In order to fully test the efficacy of the proposed design methodology under a demanding seismic scenario, three buildings of 8, 15 and 24 stories were designed in soft soil sites of Mexico City close to resonant responses. Different types or HEDDs were considered and evaluated. Pushover analyses were performed in order to verify that subject buildings may achieve the objective resilient deformation mechanism (immediate occupancy) at the maximum useful ductility capacity assumed for the HEDDs. Nonlinear dynamic analyses were performed for the complete 3D designs according to the code under the action of eight pairs of acceleration records, representative of the site where the buildings were located. This was done in order to assess maximum inelastic demands, residual drifts, and fully verify and validate the proposed resilient, structural fuse code-oriented design. From the obtained results, it is confirmed that a resilient structural performance is feasible for RC-IMFs with HEDDs under the proposed code-oriented design methodology.

In-plane cyclic response of unreinforced masonry walls retrofitted with ferrocement

Unreinforced masonries are weak against seismic loads which necessitates their retrofitting. Ferrocement is widely used as it is cheaper than alternative methods of retrofitting. Some crucial parameters can significantly affect the performance of such retrofitted structures under cyclic loading conditions, such as: aspect ratio, difference of wire mesh arrangements & pattern of retrofitting. To quantify the impact of these parameters, this study has implemented two variations of each parameter. This study conducts experimental investigations of the ferrocement retrofitted unreinforced masonry walls (URM) and evaluation of their properties such as energy dissipation, stiffness degradation, hysteretic damping, ductility, and load deformation responses. Results show notable increase in strength after ferrocement retrofitting of URM walls. Retrofitting of URM walls with inexpensive material such as ferrocement is gaining popularity, our research is guided towards finding the in-plane cyclic load characteristics of such method of retrofitting. Sample walls were prepared in two categories: (1) Long walls (aspect ratio 0.57) and (2) Short walls (aspect ratio 1). A total of ten clay masonry walls (five for each category) were constructed with reinforced concrete base slab. The first variable parameter for the tests was ferrocement coating difference. Some sample walls were retrofitted completely even the base slab & wall panel connection point while on some walls the ferrocement lamination was only applied on the wall panels. Steel wire mesh’s opening size is another crucial variable test parameter. Two different wire mesh opening sizes: (1) 3.2 × 3.6 mm and (2) 8.5 × 8.5 mm were used on the walls. One control specimen with no retrofitting for both short and long walls were prepared for test comparison purpose. Laterally reversed cyclic loads and vertical loads both were applied to the sample walls during tests. Improvements in hysteretic damping, stiffness, energy dissipation and ductility were scrutinized in particular. Finally, a comparison was drawn between the test findings and allowable load provisions prescribed in the Bangladesh National Building Code (BNBC) 1993.

Experimental study on seismic performance of hybrid steel-polypropylene fiber-reinforced recycled aggregate concrete-filled circular steel tube columns

In this paper, 1 recycled aggregate concrete-filled circular steel tube column (RACFST) and 11 hybrid steel-polypropylene fiber-reinforced recycled aggregate concrete-filled circular steel tube (HFRACFST) columns were designed given the variables of steel fiber (SF) volume content (Vsf = 0.6 %,1.2 %,1.8 %), polypropylene fiber (PPF) content fractions (Vpf = 0.05 %,0.10 %,0.15 %), concrete strengths (C40, C50, C60), thickness of steel tube (t = 2.70 mm, 3.65 mm, 4.50 mm), axial compression ratios (n = 0.25, 0.35, 0.45). Then the influence of variables on hysteretic curves, ductility, energy dissipation and stiffness degradation were studied experimentally using the pseudo-static tests. Subsequently, the restoring force models of HFRACFST were proposed based on the experimental results. The results indicated that: (1) The incorporation of HF (hybrid steel-polypropylene fiber) could enhance the hysteretic behaviour of HFRACFST columns. An increase in PPF content had little effect on the lateral bearing capacity and energy dissipation capability. Nevertheless, it could improve the ductility to some extent. As the SF content increased, the lateral bearing capacity, energy dissipation capability and ductility of the specimens increased. (2) An increase in concrete strength resulted in the increase of the bearing capacity and energy dissipation capability, but led to inferior ultimate deformation and ductility. (3) The comprehensive hysteretic behaviour was improved significantly as the thickness of steel tube increased, especially in the energy dissipation capability. (4) The specimens with higher axial compression ratio experienced inferior ultimate deformation and ductility. (5) The ductility indexes of all specimens were higher than 3.0. The yielding elastic and ultimate elastoplastic drift ratios were in the ranges 0.012–0.013 and 0.038–0.054, respectively. The hysteretic performance of HFRACFST columns could satisfy the requirement of seismic design. It is feasible to apply the HFRACFST columns to vertical load-bearing structures in the seismic zones.

Seismic performance of an assembled self-centering buckling-restrained brace and its application in arch bridge structures

Aiming to reduce residual deformation, herein, we propose the design concept of a self-centering buckling-restrained brace (SC-BRB) applied to the structural fuse of arch bridge structures. First, a novel assembled SC-BRB with combined disc springs is proposed. Notably, the hysteretic curve characteristics can be effectively controlled by the ratio of the BRB system load capacity to the SC system preload. The construction and operating mechanism of the novel SC-BRB are described, and a theoretical hysteretic model under cyclic loading is derived. Five SC-BRB specimens with different combinations are designed and fabricated. Through quasi-static tests, the characteristics including residual deformation and hysteretic energy dissipation are analyzed and compared to explore the self-centering effect and damage mode. The test results reveal that the hysteresis curve of the assembled SC-BRB is characterized by an apparent flag-type form and stable hysteretic performance. The combined disc spring significantly reduces the residual deformation of the brace, resulting in an apparent self-centering effect. The theoretical hysteretic model proposed in this paper agrees well with the test results. Finally, a comparative analysis is conducted on the seismic performance of a concrete filled steel-tube (CFST) arch bridge structure with three types of lateral braces: SC-BRB, BRB, and an ordinary brace. The OpenSees analysis results demonstrate that the CFST with the SC-BRB demonstrates better performance in terms of the displacement response and residual deformation compared with the other two CFSTs.

Performance of box-shaped column connection achieved with local grouting and bolts

To prevent the traditional box-shaped column flange connection from affecting the facade of the overall structure, this study proposed a box-shaped column connection achieved by local grouting and bolts. One integral box-shaped column specimen and two box-shaped column connection specimens were designed. The seismic performance of the connection and the influence of local grouting on the mechanical performance of the connection were studied. The failure phenomenon of the specimen was observed, and the mechanical performance of specimens, such as hysteretic behavior, bearing capacity, stiffness degradation, ductility, and energy dissipation capacity were examined. Results are as follows: the failure mode of the integral box-shaped column specimen and the specimen connected by local grouting and bolts is plastic hinge failure; the effect of local grouting can improve the integrity of the connection and obtain good energy dissipation capacity; the effect of local grouting can increase the bearing capacity of specimen by 24.84% and reduce the bolt tensile force by 34.37%; the steel connector at the column–column joint prevented the buckling deformation of the box-shaped column; the ductility is increased by 22.06%; no slip occurred between the upper and lower steel connector. Therefore, the new joint is safe and reliable. Through numerical simulation analysis, the research results show that the joint can be equivalent to rigid connection. The peak bearing capacity of the box–column joint is checked according to the Code for Seismic Design of Buildings: GB50011–2010. The calculation results are consistent with the experiment results.

Pseudo-Dynamic Test on Composite Frame with Steel-Reinforced Recycled Concrete Columns and Steel Beams

Pseudo-dynamic tests were conducted on a 2/5-scaled, three-story, two-span frame with steel-reinforced recycled concrete (SRRC) columns and steel beams. The El-Centro earthquake waves, Taft earthquake waves, and Lanzhou artificial earthquake waves were considered as the main loads to study the seismic behavior. The failure modes, displacement and acceleration time history curves, hysteretic characteristics, energy dissipation, stiffness degradation, and inter-story drift capacity of the composite frame were analyzed. Results showed that the composite frame did not show plastic deformation during the whole test process, and the steel beams and columns basically did not yield. Under the action of three seismic waves, the displacement response, acceleration response, and restoring force response of the composite frame were increased with seismic intensity, while the hysteretic curves and energy dissipation were different as the seismic wave changed. The seismic response of the composite frame was greatly affected by the spectral characteristics of the loading ground motion and the hysteretic energy mainly consisted of recoverable elastic deformation energy. Under the action of Taft wave with the input peak acceleration of 400 gal (rare earthquake), the stiffness degradation of composite frame was the largest, which reduced to 47% of the initial stiffness. This indicated that the composite frame had good energy dissipation performance in the elastic and elastic-plastic stages, and still possessed good rigidity after a rare earthquake, fully achieving the design purpose of “no collapse in major earthquake”.

Effect of the concrete cover thickness ratio on the post-yield stiffness of bridge columns with partially unbonded unstressed steel strands

A new self-centering concrete bridge column has been developed by the authors. The proposed bridge column uses unstressed partially unbonded seven-wire steel strands as elastic elements to reduce the residual displacement of the column after a strong earthquake. This research aimed to study the effect of concrete cover thickness ratio on the cyclic behavior of the proposed column. Four large-scale column specimens were tested using lateral cyclic loading. One column was the conventional concrete bridge column. The other three columns were the proposed self-centering bridge columns with varying concrete cover thickness ratios. Test results showed that partial unbonding effectively prevented the strands from yielding. The proposed columns showed post-yield stiffness ratios higher than the conventional column. The concrete cover thickness ratio did not significantly influence the hysteretic energy dissipation and the strain responses of longitudinal reinforcement. However, it had a significant impact on the post-yield stiffness ratio. The post-yield stiffness ratio of the proposed column tended to be inversely proportional to the concrete cover thickness ratio. A relationship was proposed between the concrete cover thickness ratio and the post-yield stiffness ratio for the preliminary design of the proposed column. Based on the relationship, the cover concrete thickness ratio should not exceed 5.1% to achieve a post-yield stiffness ratio of at least 5%, as recommended in the literature to control the residual displacement of a column.

Experimental investigation of the behavior of traditional timber mortise-tenon T-joints under monotonic and cyclic loading

• Monotonic & cyclic tests on traditional cylindrical mortise-tenon timber T -joints. • Great displacement capacity but also severe pinching in hysteresis loops. • Significant difference in force capacity if tenon under shear or bending. • Behavior also influenced by inherent material variations, construction etc. Monotonic and cyclic tests on cylindrical mortise-tenon timber T-joints typical of Ottoman-period mansions in mainland Greece were carried out, aiming towards a better understanding of such connections and their influence on timber-framed wall seismic performance in numerical and experimental investigations. Configurations from the head and foot of posts were tested so that the tenon was under either combined bending and shear, or pure shear. The two types of loads led to significantly different hysteretic behavior, force and energy dissipation capacity of the examined joints. Joints with gap and under push–pull out load were also tested.

Closed-form critical response of elastic-plastic shear building with viscous damper under pseudo-double impulse for simulating resonant response under near-fault fling-step motion

A set of approximate closed-form solutions of the maximum interstory drifts under the critical pseudo-double impulse (PDI) is derived for non-proportionally damped multi-story shear building models with bilinear hysteresis. The use of PDI and the closed-form solutions efficiently and accurately enable the capture of the critical responses of elastic-plastic multi-degree-of-freedom (MDOF) systems under the one-cycle sine wave, which substitutes for the main part of near-fault fling-step motions. The formulation of the closed-form maximum interstory drifts is based on the energy balance law. In the formulation, a quadratic function approximation of the damping force-interstory drift relation is introduced together with an updated mode-controlled energy-based approach (UMEA). While UMEA was proposed in the previous paper to derive the approximate maximum interstory drifts of undamped elastic-plastic MDOF systems under the critical PDI, it is extended so that it can be applied to non-proportionally damped MDOF systems. It is demonstrated that the proposed method can estimate the maximum interstory drifts of elastic-plastic non-proportionally damped MDOF systems under the critical PDI and the corresponding one-cycle sine wave with high accuracy. The estimation by the proposed method can be conducted much more efficiently and stably than the time-history response analysis (THRA). It is also shown that the hysteretic energy dissipation is not large enough to reduce the maximum interstory drifts. Finally, it is demonstrated that the proposed method can accurately estimate the maximum interstory drifts of elastic-plastic moment-resisting frames with viscous dampers under the resonant one-cycle sine wave.

Effects of gaps on the seismic performance of traditional timber frames with straight mortise-tenon joint: Experimental tests, energy dissipation mechanism and hysteretic model

The gaps are very common in the mortise-tenon (M-T) joints of the column-frame layer for the existing ancient timber buildings, which severely threaten the whole stability and safety of the structures. To study the effects of gaps on the seismic performance of traditional timber frames with straight M-T joint. Three 1/3.2-scaled straight M-T jointed timber frames, including one intact timber frame as a contrast and two timber frames with different gaps, were fabricated using Pinus sylvestris logs, and subjected them to reversed cyclic loading tests in strict accordance with the international test standard ISO-16670. The failure modes, load-displacement hysteretic response, strength, initial elastic stiffness, ductility, and stiffness degradation of the specimens were analyzed. The energy dissipation mechanisms of the timber frames with different gaps were evaluated, based on the law of energy conservation. Results indicated that the strength, initial elastic stiffness, and hysteretic energy dissipation capacity of the timber frames with gaps decreased significantly with increasing damaged degree. The gap can weaken the ductility of the timber frame, however, the inter-story drift ratio of the timber frame with gap can reached 0.16, indicating good deformation capacity. The gap had little effect on the degradation degree of the residual stiffness of the timber frame under large displacement amplitude. When the damage degree was 10%, under large displacement amplitude, the hysteretic energy consumption, elastic strain energy, and gravitational potential energy of the timber frame approximately accounted for 54%, 16%, and 30% of the total input energy, respectively. Based on the experimental results, the empirical formulas related to key cyclic performance parameters, considering the gap effects, were established. Based on the empirical relationships of the key hysteretic parameters of the timber frame with gaps, an improved hysteretic model for a timber frame with a gap was proposed and also validated. Good agreement between the model predictions and experimental results was observed.

Improving recovery of hybrid rocking walls through locally heat-treated replaceable bars for hysteretic energy dissipation

Rocking walls continue to gain interest in seismic regions due to their ability of re-centering the building system after major earthquakes. However, they have low inherent damping, thus they are often supplemented with energy dissipating elements. A rocking wall supplemented with partially debonded longitudinal bars is named as a hybrid rocking wall (HRW). While HRWs combine re-centering with adequate energy dissipation, inspection and replacement of the energy dissipating bars may not be economically achieved after a major earthquake. This paper proposes an improvement to HRWs with the use of partially debonded longitudinal bars that are locally heat-treated to strategically concentrate hysteretic action in replaceable bar segments. The effect of the heat treatment protocol on the stress-strain properties and microstructure of reinforcing bars is investigated experimentally and a procedure for locally heat-treating standard reinforcing bars is established. Combining the experimental data of heat treatment with an analytical model for HRWs, the reversed-cyclic behavior of the proposed HRW is investigated to characterize the energy dissipation through the heat-treated bar segments, the re-centering capability of the HRW, and other key design parameters of the proposed wall system.