Displacement Ductility Capacity Research Articles

Research on the Seismic Performance of Prefabricated Bridge Piers Using UHPC Grout under an Eccentric Load

At present, research on prefabricated piers is limited to the axial compression state. However, many piers are under small eccentric compression in practical engineering. In this article, the seismic performance of ultrahigh performance concrete (UHPC)-grouted corrugated pipe-connected piers under small eccentric compression was studied. A pseudostatic test was carried out by using a prefabricated pier column model connected with UHPC-grouted corrugated pipes. The failure mechanism of the plastic hinge area of the column base was studied, and the failure mode, energy dissipation capacity, displacement ductility, and ultimate bearing capacity were compared with those of an ordinary axially compressed pier column structure. The result shows that compared to the conventional cast-in-place(CIP) pier, the overall energy dissipation capacity and the ductility factor of assembled pier with UHPC-grouted corrugated pipe-connection were decreased approximately by 5.0% and by 10%, respectively. The pinching phenomenon of the hysteresis curve of the precast pier was more obvious. When the assembled piers were under small eccentric compression, the overall energy dissipation capacity was close to that of conventional CIP piers and the ductility factor was improved by 20%. Comparison of two precast piers using the same UHPC grout connections shows that the stiffness degradation process of precast pier under small eccentric compression was similar to that under axial compression. But the ductility coefficient of precast pier under small eccentric compression increased by about 20%. The small eccentric compression caused different damage degrees in the plastic hinge zone at the bottom of the precast column. The ultimate load in the same direction as the additional bending moment was 55% lower than that of the opposite direction.

Analysis and design of mechanically spliced precast bridge columns

Reinforcement continuity in concrete members is traditionally achieved through lap splicing. An alternative is to use couplers to mechanically connect bars. Mechanical bar splices have been used in conventional and accelerated bridge construction (ABC) applications usually in capacity-protected and/or non-seismic members. Nevertheless, couplers are not currently allowed in the US national design codes to be used in the plastic hinge region of bridge columns in high seismic regions mostly due to uncertainty on their structural effects. This ban has also prevented the use of couplers as an ABC bent connection. A comprehensive analytical study was carried out to determine the effects of bar couplers on the RC bridge column seismic performance, specifically displacement capacities and demands. Modeling methods were proposed and validated against multiple test data. Subsequently, more than 950 pushover and nonlinear dynamic analyses were carried out on mechanically spliced circular and square bridge columns using the validated models. The results from the pushover analyses showed that couplers can reduce the columns displacement ductility capacity up to 45 %. A trend between the coupler length, rigidity, and the column displacement ductility capacity was established. Furthermore, the effect of couplers on the column displacement demands was found to be less than 10 % compared with unspliced columns. Finally, available design methods for mechanically spliced RC bridge columns were evaluated using test data for eight large-scale bridge columns.

Influence of Low Yield Point Reinforcement and High Toughness Concrete on Seismic Performance of the Frame

Currently, ordinary concrete and steel bars are mostly used in frames, but there is no systematic research on the impact of high toughness concrete and low yield point steel bars on the seismic performance of frames. The low-cycle repeated load test of three 1/3 ratio two-story and two-span cast-in-situ concrete frame specimens is carried out. The resilience model hysteresis characteristics, displacement ductility, and energy dissipation capacity are studied and analyzed by experiment. In addition, a comparative analysis is made between the ordinary frame and the frame with low yield point reinforcement. The restoring force model of reinforced concrete (RC) frame with low yield point reinforcement and high toughness concrete is given. The results show that the frame with low yield point reinforcement has better ductility and lateral stiffness than the ordinary reinforced concrete frame. The ductility of the frame will be improved by using high toughness concrete. The deformation ability of the members will be improved by using low yield point steel and high toughness concrete in the frame.

Experimental Study on Seismic Performance Improvement of Pile-Cap Joints in a Prestressed Concrete Solid Square Pile Using a Snap-In Mechanical Connection

ABSTRACT To improve the seismic performance of prestressed concrete solid square piles with a snap-in mechanical connection, effects of the prestressed tension control stress of PC steel rods, anchoring method and reinforcement ratio of hot-rolled steel bars on the seismic performance of the pile-cap joints in the prestressed concrete solid square piles using a snap-in mechanical connection were investigated in this article. Considering the above-mentioned effect factors, the quasi-static test was first carried out on the cap pile-cap joint specimens. Then, the seismic performance of the specimens was investigated. The results indicated that the yield load and ultimate load changed slightly, the displacement ductility increased, the stiffness decreased and the damage development rate slowed down as the prestressed tension control value decreased. When the prestressed tension control stress was reduced to 0.4 times of the standard value of tensile strength of the PC steel rods, the crack resistance moment could meet the requirements of construction and hoisting at the same time. In the process of pile cutting and anchoring, the 135° hook treatment on the end of the PC steel rods could reduce the strength degradation of the pile-cap joints during the loading process, improve the energy-dissipation capacity and slow down the damage development rate of the pile-cap joints. For the specimens with ordinary hot-rolled deformed steel bars added to the pile end, its ductility was improved, the horizontal bearing capacity, displacement ductility and energy dissipation capacity were all greatly improved, and the damage development rate was slowed down. However, the reinforcing ratio of the ordinary hot-rolled steel bars should be kept within a reasonable range. Finally, the improvement measures were proposed to improve the mechanical properties of the prestressed concrete solid square piles and pile-cap joints.

Seismic Performance of a Novel Precast Beam-Column Joint Using Shape Memory Alloy Fibers-Reinforced Engineered Cementitious Composites

A novel precast beam–column joint using shape memory alloy fibers-reinforced engineered cementitious composites (SMA-ECC) was proposed in this study to achieve self-repairing of cracks and internal damage after an earthquake. Three large-scale beam–column joints were tested under displacement reversals, including one monolithically cast conventional concrete joint, one engineered cementitious composites (ECC) reinforced precast concrete joint, and one SMA-ECC reinforced precast concrete joint. Failure mode, crack pattern, hysteretic behavior, stiffness degradation, displacement ductility, and energy dissipation capacity were compared and evaluated through a cyclic loading test. The test results showed that the ECC-based (ECC, SMA-ECC) precast joints have equivalent seismic properties to the monolithically cast concrete joint. ECC-based joints enhanced the ductility and energy dissipation capacity of the joint and, remarkably, reduced crack width. The SMA-ECC reinforced joint also exhibited instant self-healing in terms of the closure of small cracks after unloading. The self-healing performance was further evaluated through ultrasonic pulse tests, with the results showing that the use of SMA-ECC material was efficient in reducing the internal damage of beam–column joints after an earthquake.

Effect of Fiber Wrapping on Bending Behavior of Reinforced Concrete Filled Pultruded GFRP Composite Hybrid Beams.

The application of pultruded fiber reinforced polymer (FRP) composites in civil engineering is increasing as a high-performance structural element or reinforcing material for rehabilitation purposes. The advantageous aspects of the pultrusion production technique and the weaknesses arising from the 0° fiber orientation in the drawing direction should be considered. In this direction, it is thought that the structural performance of the profiles produced by the pultrusion technique can be increased with 90° windings by using different fiber types. This paper presents experimental studies on the effect of FRP composite wrapping on the flexure performance of reinforced concrete (RC) filled pultruded glass-FRP (GFRP) profile hybrid beams with damage analysis. The hybrid beams are wrapped fully and partially with Glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) composites. Hybrid beam specimens with 0° to 90° fiber orientations were tested under three- and four-point bending loads. Based on the experimental load–displacement relationship results, initial stiffness, ductility, and energy dissipation capacity were compared. The experimental findings revealed that the maximum load-carrying capacities of beams produced with pultrude profiles increased by 24% with glass wrapping and 64.4% with carbon wrapping due to the change in the damages. A detailed damage analysis is provided. Similarly, significant increases were observed in structural performance ratios such as initial stiffness and ductility ratio.

Research on the out-of-plane mechanical performance of double-face superposed shear walls with different horizontal connections

The horizontal connections play a critical role in resisting gravity and lateral loads in precast concrete sandwich panel shear wall structures and it's important to fully understand their behavior under various loading conditions. This study aims to investigate the out-of-plane mechanical behavior of double-face superposed shear walls with horizontal connections featuring different lap-spliced rebar connection configurations. Three full-scale double-face superposed shear walls were tested to investigate their out-of-plane structural performance with that of a cast-in-place shear wall in terms of failure modes, cracking patterns, strain analysis, deformation analysis, load-displacement curves, and force transfer mechanism of lap-spliced rebar connections. The double-face superposed shear walls displayed and maintained a fully composite manner until failure, and the examined three different horizontal connections can allow effective force transfer between the shear walls and the main structure. The final crack distribution and failure mode of double-face superposed shear walls were almost similar to that of the cast-in-place shear wall all exhibiting obvious out-of-plane bending failure characteristics. While the initial stiffness, ultimate bearing capacity and displacement ductility capacity of double-face superposed shear walls were higher. A mathematical model predicting the ultimate bearing capacity of the double-face superposed shear wall under out-of-plane horizontal loads was proposed.

Experiment Study on the Hysteretic Performance of a Novel Replaceable Beam-to-Column Joint with Energy-Dissipating Steel Hinge

A novel precast replaceable beam-to-column joint with energy-dissipating steel hinges was proposed for the connection of precast structures to improve the seismic performance and post-earthquake resilience. The proposed joint was installed in the predetermined plastic hinge region at beams and the flange segments of the proposed joint were weakened to achieve damage concentration. Cyclic loading tests were conducted on the proposed joint and the steel sleeve confined concrete joint to study the hysteretic performance, including failure mode, load–displacement curves, ductility, and energy-dissipation capacity. Moreover, the hystertic performance of the damage-repaired proposed joint was investigated to verify the post-earthquake resilience. Results demonstrated that the proposed joints could develop favorable failure mode with the necking rupture of the weakened steel plate in steel hinge. The damage of the proposed joint was concentrated in the energy-dissipating hinges while no serious damage was observed in the precast framing components, achieving the objective of damage concentration. Compared with steel sleeve confined concrete joint, the hysteresis curve of proposed joint was more plump while an obvious pinching effect was observed in the steel-confined concrete joint. The bearing capacity and energy-dissipation capacity of the proposed joint were about 1.25 times and 1.55 times of that for the steel sleeve confined concrete joint, respectively. In addition, the hysteretic performance of the repaired specimen was identical to the original one, with the desired failure mode caused by the fracture of the steel hinge. It was noted that the hysteretic performance of the repaired joint was better than the steel sleeve confined concrete joint. The bearing capacity was recovered at up to 96.6% of the original joint while the energy-dissipation capacity was recovered at 96.1%, indicating that the proposed joint achieved the post-earthquake resilience to a great extent.

Seismic Performance Evaluation of Highway Bridges under Scour and Chloride Ion Corrosion

Cross-river bridges located in seismically active areas are exposed to two major natural hazards, namely earthquakes and flooding. As the scour depth increases, more parts of the bridge substructure will inevitably be exposed to unfavorable conditions such as chloride ion (Cl−) corrosion. To investigate the seismic performance of highway bridges under the action of scour and Cl− corrosion, a spatial finite element dynamic model of a continuous rigid bridge was established and a Cl−-accelerated electrochemical corrosion test and quasi-static test were carried out. The results showed that a reasonable scour depth and the combination sub-factors under the joint probability density of scour action and seismic action can be obtained to establish the combined expression of the action effect. Cl− corrosion can cause a reduction in displacement ductility, load-bearing, and energy dissipation capacity, and increase inequivalent viscous damping coefficient of the columns. Seismic damage of the columns grows linearly to twice the ultimate displacement under Cl− corrosion, which becomes more significant with the increase of the reinforcement ratio.

Cyclic response of concrete frame with precast column and U-shaped composite beam

This paper aims to characterize the cyclic response of the two-storey and two-bay concrete frame with the precast column and U-shaped composite beam. 1/3-scaled cyclic tests were carried out where the axial compression ratio of centrality and edge columns was fixed as 0.3 and 0.2, respectively. Results showed that the failure of the precast frame and monolithic reinforced concrete (RC) frame to compare was governed by the crushing of concrete at column bases, showing a beam sidesway failure mechanism. The plump hysteresis loops were detected, and the overall displacement ductility of both frames was up to 4.3. The load-carrying ability, displacement ductility and energy dissipation capacity of the proposed precast frame were comparable to those of the monolithic RC frame. In addition, the numerical simulation successfully captured the failure pattern of such frames under cyclic loading, and the predicted load–displacement curves matched well with the experimental results. The parametric analysis including axial compression ratio, loading approach and composite beam type was also performed to extend the experimental work.

Cyclic behaviour of as-built and strengthened existing reinforced concrete columns previously damaged by fire

A structure, during its life, may be subjected to multiple hazards. These hazards are sometimes combined over a short period of time, or in some cases occur many years apart, with the first hazard influencing the structural response under a second hazard. A reinforced concrete (RC) structure previously damaged by fire and then exposed to seismic loading is one such example. To assess such structures, the effects of fire on the cyclic performance of RC elements needs to be better understood. Moreover, it is also important to develop and validate strengthening methods that can reinstate or improve the seismic performance of fire-damaged RC elements. This paper presents the results of a novel experimental campaign where six full-scale RC columns with detailing representing existing Mediterranean buildings designed to old seismic codes are subjected to fire and then cyclic loading. Four RC columns were damaged after exposure to 30 or 90 min of the ISO 834 standard fire curve in a furnace and then tested under uniaxial cyclic lateral loading up to failure. Two of these columns were repaired and strengthened post-fire with Carbon Fibre Reinforced Polymer (CFRP) wrapping. The strengthening method aimed to increase the concrete strength through confinement, and to increase the displacement ductility and energy dissipation capacity under seismic loading. Two additional control columns, one as-built and another strengthened, were cyclically tested for comparison with the fire-damaged columns. It was found that the 30 min fire exposure resulted in few concrete cracks, whilst cover spalling and general cracking was observed in the 90 min fire exposure. A significant decrease in the displacement ductility and dissipated energy of the columns was observed following fire exposure, even for the 30 min fire. The columns that had post-fire repair and CFRP strengthening, showed better cyclic performance than the control column without fire exposure. It was also found that post-fire strengthened columns may reach similar seismic performance than similarly strengthened columns without previous fire damage.

Effects of basalt and glass fiber composites usage for strengthening on the cyclic behavior of brick infill walls

In the current study, the effects of 10 mm bilaterally applied basalt fiber reinforced concrete (BRC) and glass fiber reinforced concrete (GRC) plasters with different fiber content (1.0%, 2.0% and 3.0%) on the behavior of the brick infill walls were investigated. For this purpose, strengthened brick infill walls placed in a hinged steel frame on all four corners were examined comparatively with their non-plastered and ordinary cement plastered conditions under cyclic loading. The load carrying capacities, displacement ductility, stiffness degradation and energy dissipation capacities of infill walls were determined using obtained results. The test results showed that brick walls with 1.0% glass fiber and 2.0% basalt fiber content showed the best performance in terms of load carrying and energy dissipation capacity. Also brick wall with 1.0% glass fiber content has the lowest stiffness degradation decrease at the ultimate drift ratio. In addition to all these, it has been observed that the mechanical behavior of the walls strengthened with plasters containing different percentages of fiber has improved considerably compered to non-plastered and ordinary cement plastered brick walls. This situation reveals that basalt and glass fiber plasters can be used to strengthen the walls. It is recommended that this method can be used quickly and effectively in the reinforcement of masonry structures, which have a large amount in the existing building stock.

Cyclic behavior of semi-rigid steel frame infilled with damping wall panels

Semi-rigid connected steel frame is characterized by excellent displacement ductility and energy dissipation capacity, while detrimental infill-frame interaction from the traditional infill would be a key role in seismic behaviors for such steel frames and may damage both infill and steel frame. In this study, the solution to partition the infill with low-strength mortar sliding joints and uncouple the infill from the surrounding frame by flexible connections for the semi-rigid steel frames is presented. Three specimens designed in this context were examined experimentally and numerically. The test results show that the frame with low-strength sliding joints and flexible connections behaves similarly to the bare steel frame, and improves the energy dissipation capacity by about 19.83%. Unlike the semi-rigid steel frame with traditional infill, significant crack of the infill or local stress concentration on the columns is undetected even at a drift ratio of 3.33% in the proposed infilled steel frame. Parametric analysis results confirm that the friction factor of the low-strength sliding joints is the key parameter to improve the lateral bearing capacity of the infill system.

Experimental study on seismic performance of prefabricated viscoelastic damping bolted joints

Aiming at the defect of insufficient bearing capacity of prefabricated concrete beam-column joint with bolted connection, a prefabricated viscoelastic damping bolted joint (VDBJ) is proposed with good seismic performance. The damping principle is based on that viscoelastic (VE) dampers can provide energy dissipation and additional stiffness for the structures. Three full-scale beam-column joint specimens were designed, including one cast-in-place joint specimen, one prefabricated bolted joint specimen without VE dampers and one prefabricated bolted joint specimen with VE dampers. Since the viscoelastic damper is a passive energy dissipation device with velocity correlation, comparison and analysis of three specimens under high-frequency cyclic loading are performed on the failure modes and seismic performance indexes such as hysteretic energy dissipation, displacement ductility, stiffness degradation and ultimate bearing capacity. The analysis of the test results indicate that the proposed prefabricated viscoelastic damping bolted joint has stronger ultimate bearing capacity and displacement ductility than the cast-in-place joint. The arrangement of VE dampers effectively controls the appearance and expansion of concrete cracks, which not only achieves the expected effect of shock absorption and energy dissipation, but also can realizes the rapid replacement of components after the earthquakes.

Seismic performance of glued-laminated wood frame and frame brace structure: Experimental and finite element analysis

The glued-laminated wood frame structure has the problems of insufficient bearing capacity, low lateral stiffness and low energy dissipation, which adversely affect the seismic performance of the structure. In order to improve the seismic performance of the structure, quasi-static tests were conducted on three glued-laminated wood frames to study their cyclic behavior, the failure pattern, bearing capacity, displacement ductility, stiffness degradation and energy dissipation capacity in detail. The test results showed that the hysteresis curves of the three specimens were not full, showing a typical “pinching” characteristic. The addition of flange stiffeners (Specimen TFB) and additional wood braces (Specimen TFBT) significantly improved the lateral bearing capacity, ductility characteristics and cumulative energy dissipation of the glued-laminated wood frame (Specimen TFA). In addition, the finite element models were established and compared with the test results. The simulation result showed that the modeling of the three specimens can fully reflect the hysteretic characteristics of the specimen pretty well. Reducing the beam-to-column stiffness ratio, increasing the wood brace cross-sectional area and increasing the bolt diameter can improve the lateral bearing capacity of the glued-laminated wood frames in various degrees.

Performance evaluation of a RC frame structure from element level to structure level

Ductility is an important design parameter which controls the flow of plasticity in a structure to improve the ability to sustain severe load with nonlinear deformation. In the present study, the flow of ductility from element level to structure level has been assessed. For the study purpose, a RC frame structure has been considered and the displacement ductility capacity of the frame has been evaluated from the best possible combinations of curvature and rotation ductility capacity of beams and columns. To generate the capacity curve of the structure, nonlinear static pushover analysis has been performed. It has been observed that the variation of section ductility of the column is more significant with diameter and spacing of the transverse reinforcement bar than the same for beam section. A reduction of structural ductility has been observed as compared to the element ductility which needs more detailing requirement for the fulfillment.

Collapse strength ratios for weak first-story buildings under soft soil intraslab earthquakes

Weak first-story buildings are susceptible to experience severe structural damage, and even collapse, during strong earthquakes as was evidenced during the September 19, 2017 (Mw = 7.1) intraslab earthquake that hit Mexico City. Such type of buildings are prone to exhibit a negative slope in their capacity curve due to weak first-story mechanism that might lead to dynamic instability during earthquake excitation. Therefore, this paper presents the main results of an investigation focused on evaluating the collapse strength ratios, Rc (i.e., the normalized lateral strength ratio in the onset of dynamic instability) of single-degree-of-freedom (SDOF) systems whose force-displacement nonlinear envelope (backbone) behavior is representative of that observed in existing multistory weak first-story buildings. Particularly, their envelope exhibit several levels of negative slope after a post-yield displacement ductility capacity. Median and dispersion of Rc ratios were obtained for degrading SDOF systems subjected to a set of 136 earthquake ground motions recorded in soft soil sites of Mexico City from instraslab earthquakes. Results of this investigation showed that Rc ratios depend on the normalized period of vibration with respect to the predominant period of the ground motion, T/Tg, the displacement ductility capacity, μc, and the negative slope after peak strength, αc. Additionally, the spectral trend of Rc ratios at soft soil sites is different to that reported for firm soil sites. A continuous functional form is introduced to obtain estimates of median Rc ratios for the preliminary seismic assessment of weak first-story buildings in this seismic environment.

Study on Finite Element Model of the Prefabricated Reinforced Concrete Beam-Column Joints with Grouted Sleeves

Based on the monotonic tensile test of grouted sleeve specimens conducted, this paper uses multifactor regression analysis to construct the equivalent constitutive relationship of grouted sleeve specimens under uniaxial tension. The study based on this constitutive relationship of grouted sleeves and the effect of bond and slip between steel and concrete were considered. The prefabricated reinforced concreted beam-column joints with grouted sleeves were presented with finite element software ABAQUS. The seismic behavior of prefabricated reinforced concreted beam-column joints with grouted sleeves under low-frequency cyclic loading was then investigated. In addition, parametric studies via finite element analysis were performed to examine the influence of various parameters on the strength and energy dissipation capacity of the specimens. The simulation results show that plastic deformation was mainly observed near the beam-column interface; the hysteretic curve of this joint was plump. The test results showed that good energy dissipation and displacement ductility capacities can be achieved. The error of yield load between the numerical simulated and experimental result was 7.11%, the error of peak load was 6.88%, the error of ultimate load was 3.76%, and the error of displacement ductility was 7.84%. Results showed that the calculated results obtained in the paper agree well with test results from the references. The finite element model adopted in this paper can reflect the seismic behavior of the prefabricated reinforced concrete beam-column joints with grouted sleeves by using equivalent constitutive relation.

Experimental study on seismic performance of strengthening masonry wall using hybrid fiber-reinforced reactive powder concrete

An experimental study was conducted to investigate the seismic performance of masonry walls strengthened using hybrid fiber-reinforced reactive powder concrete (HyFRRPC) as a coating. The proposed reinforcement technique was employed to improve the overall strength and structural integrity of the confined masonry wall. In order to guarantee the composite action between the masonry substrate and the coating material, material tests were conducted to achieve an optimal mixture for the HyFRRPC. Then, six full-scaled confined masonry specimens strengthened by HyFRRPCs with varied strengthening configurations were tested under in-plane quasi-static horizontal loading. The test and analysis results indicated that the proposed HyFRRPC-strengthening technique can effectively improve the lateral carrying capacity, displacement ductility, and energy dissipation capacity of masonry walls, and provide an optimal reinforcement. Finally, a simplified analytical model was also proposed for practical application.

Mechanical properties and seismic behavior of confined masonry walls in freeze-thaw environment

Previous literatures show that freeze-thaw cycles (FTC) will deteriorate the physical and mechanical properties of masonry materials. The research in this paper focused on the influence of FTC on mechanical properties and seismic performance of confined masonry walls. A series of mortar cubes, brick units and double-shear specimens built of concrete brick and three types of mortar (cement, cement-lime and cement-fly ash) were subjected to testing after rapid freeze-thaw experiment in environmental chamber. Besides, quasi-static tests were performed on four confined masonry wall specimens to investigate their seismic behavior under varying degrees of freeze-thaw damage. The test results indicated that as the number of FTC increased, the compressive strength of mortar and bricks, masonry shear bond strength, load-carrying capacity, displacement ductility, secant stiffness and energy dissipation capacity of confined masonry walls all shown a downward trend. In addition, a prediction model was proposed to obtain the degradation of shear bond strength of masonry subjected to freeze-thaw damage, and could be used in the rapid investigation and non-destructive detection. Moreover, the addition of fly ash was helpful to slow down the deterioration of masonry buildings in freeze-thaw environment.