Displacement Ductility Capacity Research Articles

Behavior of Glulam Columns Reinforced by Near-Surface-Mounted CFRP Laminates under Eccentric Compression Loading

This paper introduces simple glued laminated (glulam) timber columns reinforced by near-surface-mounted carbon-fiber-reinforced polymer (CFRP) laminates (GTMC columns). Twenty-four columns were fabricated and tested under eccentric compression loading to validate the effectiveness of this kind of column. In accordance with the degrees of eccentricity, specimens were divided into three groups. In each group, one column without inlaid CFRP laminates served as a control column, while the others were inlaid with CFRP laminates. All columns were tested for ultimate load capacity, displacement ductility, failure mode, and energy dissipation capacity. Test results show that inlaid CFRP laminates are effective in increasing ultimate load capacity and deformability. Meanwhile, the corresponding analytical model was also derived to predict the ultimate load capacity of GTMC columns. A comparison of the predicted and tested ultimate load capacities demonstrated that the analytical model is generally able to evaluate the ultimate load capacity of GTMC columns with an average underestimation of 8.7%. Furthermore, a finite-element analysis was conducted to investigate the effects of thickness and mounted depth of CFRP laminates on ultimate load capacity and initial stiffness.

Seismic performance of RC-column wrapped with Velcro

A seismic strengthening method using Velcro is proposed to improve the seismic performance of columns in RC frame structures. The proposed method was evaluated experimentally using three fabricated RC specimens. Velcro was wrapped around the columns of the RC-frame specimen to prevent concrete spall falling. The reinforcing performance of the Velcro was determined from comparison of results on seismic performance (i.e., strength, displacement, failure mode, displacement ductility capacity and amount of dissipated energy). As the displacement of the reinforced specimens was increased, the amount of dissipated energy increased drastically, and the displacement-ductility-capacity of the reinforced specimens also increased. The final failure mode of RC frame structure was changed. As a result, it was concluded that the proposed seismic strengthening method using Velcro could be used to increase the displacement ductility of RC columns, and could be used to change the final failure mode of RC-frame structures.

Updating the Seismic Reliability of Existing RC Structures in a Marine Environment by Incorporating the Spatial Steel Corrosion Distribution: Application to Bridge Piers

AbstractAlthough several models are available for evaluating the structural performance of corroded reinforced concrete (RC) structures, seismic reliability assessments considering the effect of steel corrosion are currently scarce. Determining how long existing RC structures in an aggressive environment will be able to have a seismic safety level greater than the threshold remains difficult. Life-cycle reliability assessments of these structures under seismic hazards and hazards associated with airborne chloride are discussed in this paper. When predicting the seismic reliability of existing RC structures, observational data from inspection and/or nondestructive testing methods could be used to estimate the current material corrosion level. Considering the effect of steel corrosion in the plastic hinges of deteriorating structures on their seismic capacity is important. The displacement ductility capacity at the occurrence of longitudinal buckling of rebar in RC structures depends on the steel corrosion ...

Seismic Performance of Different Masonry Buildings: Full-Scale Experimental Study

AbstractFull-scale single-room masonry buildings of different typology, i.e., unreinforced (URM), reinforced (RM) and Confined Masonry (CM) were tested under cyclic loading in quasi-static manner to study the seismic performance. All the indigenously built building typologies were 3.01×3.01 m in plan and 3.0 m in height, having exactly similar material, geometry, and construction practices. Among six tests conducted, three were on original masonry system and remaining three models were URM-repaired (URM_REP), URM-retrofitted (URM_RET) and RM-retrofitted (RM_RET), with same initial features. The observations made and the test data collected were for different damage grades and displacement capacity. The present paper focuses on the analysis of experimental results in terms of lateral load capacity, stiffness degradation, displacement ductility capacity, behavior factors and energy dissipation capacities. The failure modes observed were: sliding of brick at mortar-unit interface; discrete shear cracks in m...

Large-Scale Test of a Modular Steel Plate Shear Wall with Partially Encased Composite Columns

AbstractAs part of an experimental study on the behavior of steel plate shear walls with partially encased composite columns, a large-scale modular specimen was tested at the University of Alberta to observe and quantify some important parameters related to seismic design of this type of structure. The two-story one-bay specimen was subjected to cyclic load until it failed. It was shown that the modular construction method used to build the specimen had very little effect on the overall behavior. The specimen exhibited high initial stiffness, good displacement ductility and high energy dissipation capacity. The observations during the test indicated that the detailing of the composite columns played an important role in improving the seismic performance of the specimen. Based on the results of the current experiment and previous studies, design and detailing recommendations have been made.

Seismic Response Evaluation of Ductile Reinforced Concrete Block Structural Walls. I: Experimental Results and Force-Based Design Parameters

The reported experimental study documents the performance of six fully grouted reinforced concrete block structural walls tested under quasistatic cyclic loading. The walls fall under the ductileshear walls and the special reinforced masonry walls seismic force resisting system (SFRS) classification of the Canadian and U.S. standards, respectively. The test matrix consisted of one rectangular, one flanged, and two slab-coupled walls, all with an overall aspect ratio of 1.4. In addition, two rectangular walls, representing the individual components of the slab-coupled wall systems, were tested to quantify the wall slab coupling effects. In addition to discussing the experimental results, the study also presents key force-based seismic design (FBSD) parameters, such as the wall lateral load capacity, plastic hinge length, wall failure modes, and displacement ductility capacities. Moreover, the effects of wall cross-sectional configuration and slab coupling on the cyclic response and deformation capabilities of the walls are discussed. In general, the yield and ultimate loads were found to be accurately predicted using the Canadian Standards Association (CSA) S304-14 and Masonry Standards Joint Committee (MSJC) formulations. The wall experimental displacement ductility values (calculated at 20% strength degradation) ranged between 5.4 and 7.6, whereas the idealized displacement ductility values at the same strength degradation level ranged between 3.4 and 5.4. The analysis results reported in the paper highlight the fact that walls designed and detailed within the same SFRS classification possess significantly different FBSD parameters. The results also indicate that slab coupling, although not recognized as a wall coupling mechanism in the current editions of the CSA and MSJC, can have significant influences on the seismic response of ductile/special reinforced masonry wall systems.

Quasi-Static Cyclic Testing of Elevated RC Pile-Cap Foundation for Bridge Structures

In current practices, the elastic design principle for the seismic design of pile foundations is an overly conservative strategy. In this regard, cyclic lateral loading tests were conducted to investigate the seismic failure mechanism and ductile behaviors of elevated RC pile-cap foundations. Two six-pile specimens with different aboveground heights were constructed and embedded in a single layer of cohesionless soil. Hysteretic characteristics and observed damages of the pile groups were presented, together with the corresponding soil pressure and pile curvature responses. From the test results, the sequence and positions of the pile plastic hinges were established. Ultimate limit states of the pile groups were determined according to test data, as well as numerical analysis results. Test results revealed a ductile flexural failure mode for both specimens. Plastic hinges were detected first at the top of outer piles, then underground at a depth of 4–6 times the section width. A displacement ductility capacity of 3.5 was observed for the elevated pile-cap foundation. Test results also indicated a linear relation between the displacement ductility factor and the cap rotation, which was important for determining the displacement at the top of piers.

Assessment of seismic design parameters of moment resisting RC braced frames with metallic fuses

A parametric study was devoted to evaluate, using static nonlinear analyses (pushover), global seismic design parameters for low to medium rise regular reinforced concrete moment-resisting braced frames (RC-MRBFs) with hysteretic energy dissipation devices mounted on chevron steel bracing. Frame models with range from five to twenty five stories were designed using different elastic stiffness ratios between the moment frame system and the whole structure (frame-bracing-hysteretic device system). Also, different elastic stiffness balances between the hysteretic device and the supporting braces were considered. Different post to pre yielding stiffness ratios for the hysteretic devices were considered. Two angles of inclination of the chevron braces with respect to the horizontal axis were considered, taking into account typical story heights and bay widths used in Mexican practice. From the results obtained in this study, stiffness balances are defined to achieve a suitable mechanism where the hysteretic devices yield first and develop their maximum local displacement ductility, whereas in the moment frame incipient yielding is only formed at the beam ends. Finally, additional comments are made with respect to: (a) relations between global ductility capacity and local displacement ductility capacity for the hysteretic devices for a given combination of the studied stiffness parameters and angles of inclination, (b) story drifts at yielding and their relation with the selected elastic stiffness ratio between the moment frame system and the whole structure and, (c) overstrength factors for design purposes.

EXPERIMENTAL STUDY OF SEISMIC PERFORMANCES OF RC BRIDGE COLUMNS WITH CFST COLUMN EMBEDDED LNSIDE

To improve the seismic performances of reinforced concrete (RC) bridge columns and to prevent columns from shear failure and core concrete crushing, high strength concrete filled steel tube (CFST) is put into RC columns to form a new kind of composite column. Through cyclical loading tests, the seismic performances of four columns are studied. The first column tested is a conventional RC column, the second one is a bonded composite column, the third one is an unbonded composite column, and the fourth one is an unbonded composite column whose axial force is composed of only bone by its CFST column. The test results show that the CFST column can increase the flexural strength, displacement ductility and energy dissipation capacity, and decrease the residual displacement after undergoing large deformation. When the degree of bond between the steel tube and the outside concrete around the tube is reduced, the load-carrying capacity of the composite column decreases, but the ductility increases. When the axial force is only bone by the CFST column, the load-carrying capacity of the composite column decreases significantly, and the ductility increases markedly.

Monotonic behavior of large-scale SFRC beams without stirrups

An experimental study is conducted on four reinforced concrete (RC) and steel-fiber reinforced concrete (SFRC) large-scale beam specimens to study their ultimate flexural strengths, crack propagation, failure mechanisms, energy dissipation, and ductility response under the monotonically-increased loading. All test specimens are geometrically-similar having the exactly same dimensions, concrete grade, percentage of longitudinal reinforcement, shear span-to-depth ratio, and grade of steel. End-hooked steel fibers of aspect ratio 80 and volume fraction ranging from 1.0% to 1.5% are used in the specimens. In case of SFRC specimens, one-half portion consists of SFRC mix without transverse stirrups, whereas the other half is filled with plain concrete with transverse stirrups. Test results showed that the addition of steel fibers enhanced the ultimate flexural strength, displacement ductility, curvature, and energy absorption capacity of the specimens. As the fiber content is increased, the deformability of the flexural members is also increased and crack width is reduced at the higher load levels. However, a minor reduction in the ultimate flexural resistance is noted in the SFRC members in excess of 1.0% fiber content. Further, the failure mechanism is controlled by the combined shear and flexural action in the SFRC specimen with 1.5% fiber content.

Displacement ductility for seismic design of RC walls for low-rise housing

The paper compares and discusses displacement ductility ratios of reinforced concrete walls typically used in one- and two-story houses. Ductility is investigated by assessing response measured on 39 walls tested under shaking table excitations and quasi-static lateral loads. Variables studied were the height-to-length ratio and walls with openings, type of concrete and, steel ratio and type of web reinforcement. An equation to estimate the available ductility of a wall is proposed. Based on statistical analysis of data, values of displacement ductility capacity are recommended. Displacement ductility ratios can be used to compute both strength modification and displacement amplification factors for code-based seismic design.

Response of partially-restrained bolted beam-to-column connections under cyclic loads

The structural response of steel moment resisting frames (MRFs) is greatly dependent on the behavior of beam-to-column joints, according to a properly detailed beam-bolts-plates-column structural chain, in light of capacity design principles. A modeling procedure for bolted top-and-seat angle components and connections for potential use in seismic MRFs is presented herein. Although these partially-restrained (PR) connection systems have been demonstrated to provide economic savings, they are not currently certified to be used for moment resistance in any major building specification jurisdiction. Examples of full-scale moment resisting connection systems, experimentally tested in past programs, have been numerically analyzed, focusing on top-and-seat angle components, which were observed to control the global response of the joint in terms of failure mechanisms, limiting the displacement ductility capacity and dissipation energy capabilities of the whole resisting system. Refined nonlinear solid FE models, accounting for the influence of friction, pretension of bolts, prying and relative slippage of components through highly nonlinear contact elements, have been developed to reproduce the cyclic-reversal test protocol. Simplified approaches, based on one-dimensional inelastic force-based fiber elements, combined with nonlinear links, to globally represent connection elements interaction, have been developed and validated by comparisons with experimental response.To propose an alternative and conservative method for quick rotational stiffness estimates of these PR bolted top-and-seat angle connections, a series of detailed parametric solid FE analyses have been performed and the effectiveness of this analytical preliminary-design-stage tool quantified in comparison with some of the most commonly known analytical approaches.

Seismic Performance of Column-Footing Connection of Modular Pier using CFT

CFT 기둥은 시공이 간단하고 경제적이며 구조성능이 우수한 현장타설 매입형 연결 형식이다. 본 연구에서는 모듈러 교각에 적용되는 CFT 기둥-기초 연결부 형식을 제안하고, 실험을 통하여 구조성능을 평가하였다. 기둥-기초 연결부의 구조성능을 평가하기 위해서 기초부 콘크리트에 매입되는 CFT 기둥의 매입깊이를 변수로 총 4개의 실험체를 제작하여 실험을 수행하였다. 준정적 실험결과, 매입깊이가 0.6D인 실험체에서는 낮은 하중단계에서 기초부의 콘파괴로 인하여 상대적으로 낮은 연성능력을 보였다. 그러나 매입깊이가 0.9D 이상인 실험체에서는 기초부의 콘파괴가 방지되고 CFT 기둥 하단부에서 전형적인 휨파괴 거동을 보이며 높은 연성능력을 발휘하였다. 하중-변위 이력곡선, 변위 연성도 및 에너지 소산능력 등을 분석한 결과, 제안된 CFT 기둥-기초 연결부의 매입깊이는 0.9D~1.2D 수준이 내진성능을 발휘하는 합리적인 수준인 것으로 평가되었다. The CFT (Concrete Filled steel Tubes) column-footing connection is cast-in-place embedded type which provides simple construction procedure, low cost, and superior structural performance. In this study, CFT column-footing connection of modular pier is proposed and structural performance is evaluated by experimental tests. To evaluate structural performance of the CFT column-footing connection, a series of experimental tests were performed for the 4 specimens with different embedded depth. As a result of the quasi-static test, the specimen with 0.6D (0.6 times the outside diameter of steel tube) embedded depth showed relatively low ductility than other specimens with larger embedded depth due to cone failure of base concrete occurred during the lower loading step. On the contrary, cone failure of the base concrete was not observed in the specimens with larger embedded depth than 0.9D, but typical flexural failure in lower part of CFT column was observed. With the analyses of force-displacement curve, displacement ductility, and energy dissipation capacity, it is concluded that the rational range of embedded depth of the CFT column-footing connection is from 0.9D to 1.2D in view of good seismic performance.

Seismic responses of composite bridge piers with CFT columns embedded inside

Shear failure and core concrete crushing at plastic hinge region are the two main failure modes of bridge piers, which can make repair impossible and cause the collapse of bridge. To avoid the two types of failure of pier, a composite pier was proposed, which was formed by embedding high strength concrete filled steel tubular (CFT) column in reinforced concrete (RC) pier. Through cyclic loading tests, the seismic performances of the composite pier were studied. The experimental results show that the CFT column embedded in composite pier can increase the flexural strength, displacement ductility and energy dissipation capacity, and decrease the residual displacement after undergoing large deformation. The analytical analysis is performed to simulate the hysteretic behavior of the composite pier subjected to cyclic loading, and the numerical results agree well with the experimental results. Using the analytical model and time-history analysis method, seismic responses of a continuous girder bridge using composite piers is investigated, and the results show that the bridge using composite piers can resist much stronger earthquake than the bridge using RC piers.

Displacement Ductility Capacity Assessment for a Fixed-Head Pile in Cohesionless Soil

AbstractThis study develops assessment formulas for the displacement ductility capacity of a fixed-head pile in cohesionless soils. The derivations of the formulas are based on an ideal model of a semiinfinite nonlinear pile in a Gibson soil, whose subgrade reaction modulus increases linearly with depth, to link the displacement ductility capacity of the pile with the pile–soil system parameters. The parameters in the formulas include the sectional overstrength ratio and curvature ductility capacity, as well as a modification factor for considering soil nonlinearity. The modification factor is a function of the displacement ratio of the pile’s ultimate displacement to the effective soil yield displacement, which is constructed through a number of numerical pushover analyses. The format of the formulas is similar to that for a pile in cohesive soils. For the case of linear soil, the formulas provide a lower-bound estimate of pile ductility capacity; the displacement ductility capacity of a pile in cohesion...

Experimental Study on Seismic Performance of CFRP Strengthened RC Frames Damaged by Earthquake

In this paper, we carried out low cyclic loading test over CFRP strengthened seismic-damaged RC frame named KJ-2 with the quasi-static test method, and compared the seismic performance with the same sections and materials RC frame named KJ-1 which was unstrengthened. We study the seismic performance such as hysteresis curve, skeleton curve, stiffness degradation, bearing capacity degeneration, displacement ductility, and energy dissipation capacity of the reinforced RC frame. On this basis, we analyzed the results of this test in order to obtain some guiding opinions for asymmetric span RC frames that strengthened by CFRP, and provide main preference basis or future national or industry standards.

Behavior and modeling of superelastic shape memory alloy reinforced concrete beams

The re-centering phenomenon of superelastic Shape Memory Alloy (SMA) reinforced concrete is a unique characteristic that is appealing for structural applications, along with the ability to respond with stable hystereses and achieve similar strength and ductility to concrete reinforced with conventional deformed bars. The objective of this study was to investigate the structural performance of superelastic SMA reinforced concrete and to develop a preliminary constitutive model applicable to nonlinear finite element algorithms. Seven simply supported flexure-critical concrete beams, reinforced with either SMA bars in the critical region or conventional deformed reinforcement, were subjected to monotonic, cyclic, and reverse cyclic loading. The experiment results demonstrated the superior capacity of the SMA beams to recover inelastic displacements. The SMA beams sustained displacement ductility and strength capacity comparable to the conventional beams. Crack widths and crack spacing were larger in the SMA beams; however, upon removal of load, the crack openings were recovered. Energy dissipation was lower in the SMA beams, particularly when subjected to reverse cyclic loading. The constitutive model based on a trilinear backbone envelope response and linear unloading and reloading rules provided satisfactory simulations.

Risk-Based Approach for Optimum Maintenance of Bridges under Traffic and Earthquake Loads

Structures deteriorate as a result of material aging, aggressive environmental conditions, and increasing loads. During their lifetime, structures are also possibly exposed to some extreme events. The associated consequences of failure caused by progressive deterioration or extreme events can be devastating. Therefore, risk assessment and risk mitigation are necessary to keep structural performance within tolerable levels. This paper proposes an approach for assessing the time-dependent risks caused by traffic and earthquake loads and establishing the optimal preventive and essential maintenance strategies of bridges. The efficiency of the proposed approach is demonstrated using a highway bridge. Socioeconomic and environmental losses are investigated in a consequence-based framework. The vulnerability analysis under traffic loads is performed using time-dependent deterioration and traffic load models. The time-dependent failure probability for given earthquake loads is computed by comparing displacement ductility capacity and demand obtained via nonlinear dynamic analysis. The risks from 196 earthquake scenarios associated with four magnitudes and 49 earthquake strike locations are compared, and the highest one is selected as representative of the seismic risk. Based on the available maintenance options and the associated costs, the optimal lifetime essential/preventive maintenance strategies for total risk mitigation are developed.

Investigating Influencing Factors on the Ductility Capacity of a Fixed-Head Reinforced Concrete Pile in Homogeneous Clay

AbstractThis study performs parametric analyses on the displacement ductility capacity of a fixed-head reinforced concrete pile in homogeneous clay, considering the spread of plasticity in the pile. The parametric study regards the pile as a limited ductility structure, which conditionally allows the pile to have inelastic response during large loading. The variables considered include the pile section parameters andp-ymodel parameters. A large number of pushover analyses are conducted to examine the displacement ductility capacity of the pile. The results show that the plastic hinging will occur at the pile head region for a fixed-head pile, and the displacement ductility capacity of the pile is mainly influenced by the over-strength ratio of the pile section. Furthermore, the second plastic region may occur in ground when the axial force is in high tension. Based on the design concept of limited ductility structures, the high tensile force in pile should be avoided in pile design. A quantitative relationship between the displacement ductility capacity and over-strength ratio is suggested for engineering applications.

Experimental Study of Glued Laminated Guadua Bamboo Panel as an Alternative Shear Wall Sheathing Material

Wood frame buildings have shown good performance on past earthquakes mainly because the lateral system of those buildings was able to dissipate energy without significant loss of lateral capacity. Typically, the lateral load resisting system is provided by wood shear walls, which consist of a wood frame sheathed with wood or wood-based composites, such as Plywood or OSB panels. Taking into account the increasing forest demand for wood, there is a global need to find alternative energy-efficient, renewable and eco-friendly construction materials. Giant bamboo like Guadua Angustifolia kunt emerges as an interesting construction material, since it has a fast growing rate (3 to 4 years), high strength to weight ratio and high carbon (CO2) capture capabilities. Results of a past study conducted at the Universidad de los Andes in Bogotá-Colombia reported that Glued Laminated Guadua Bamboo (GLG) has mechanical properties comparable to those of the best structural timbers in Colombia. Potential applications of GLG include not only laminated beams and columns, but also structural panels to be used as a sheathing material for wood frame shear walls. A comprehensive experimental study has been performed on GLG sheathed shear walls in order to find an alternative sheathing material for wood frame buildings as well as to explore their possible application for residential and/or commercial construction in Colombia. A series of tests were conducted on full-size shear wall specimens in order to study the influence of the wall aspect ratio and the edge nail spacing on the shear wall performance. Based on cyclic tests on shear walls, it was found that the stiffness and maximum load carrying capacity of the wall increases as edge nail spacing decreases. In contrast, the displacement ductility capacity decreases, since the rotation of the panels is restricted when the edge nail spacing is reduced. Experimental results also revealed that stiffness, maximum load capacity, and ductility of the GLG sheathed shear walls are not affected by the aspect ratio of the wall. The final stage of the present study included dynamic shake-table tests on full-size one and two-story housing units using GLG sheathed shear walls. Results showed that the units had similar performance characteristics to those of OSB and Plywood sheathed shear walls, and it was concluded that wood-GLG combination could be a viable construction alternative from a structural point of view.