31 research outputs found
Seismic failure probability and vulnerability assessment of steel-concrete composite structures
Full text linkBuilding collapse in earthquakes caused huge losses, both in human and economic terms. To assess the risk posed by using the composite members, this paper investigates seismic failure probability and vulnerability assessment of steel-concrete composite structures constituted by rectangular concrete filled steel tube (RCFT) columns and steel beams. To enable numerical simulation of RCFT-structure, the details of components modeling are developed using OpenSEES finite element analysis package and the validation of proposed procedure is investigated through comparisons with available experimental results. The seismic fragility and vulnerability curves of RCFT-structures are created through nonlinear dynamic analysis using an appropriate suite of ground motions for seismic loss assessment. These curves developed for three-, six- and nine-story prototypes of RCFT-structure. Fragility curves are an appropriate tool for representing the seismic failure probabilities and vulnerability curves demonstrate a probability of exceeding loss to a measure of ground motion intensity
بررسی آزمایشگاهی رفتار دیوار برشی کوپله با استفاده از بتن الیافی توانمند HPFRCC در تیر رابط با آرایش آرماتور گذاری متفاوت
No full textCoupling beam is as the first line of defense in the coupling shear walls and it acts as a shear fuse and is important to improve the seismic behavior of any structure. Coupling beams made of high performance fiber reinforced cementinous composite (HPFRCC) are capable alternatives compared to traditional concrete and result into increasing capacity and ductility and also reducing the congested amount of longitudinal and transverse and diagonal reinforcement. The design of coupling beams, with span-to-depth ratios that often range between 1.5 and 3.5, requires a special attention due to the large inelastic rotations and shear stress coupling beams can be subjected during a strong earthquake. In order to ensure adequate seismic performance, ACI Building Code (318-08) provisions for coupling beams in regions of high seismicity include the use of diagonal reinforcement designed to resist the entire shear demand, together with special column-type transverse reinforcement confining either the diagonal bars or the entire member.This paper investigates an experimental study on cyclic behavior of three concrete coupling beams with span to height ratio equal two. The first specimen with regular concrete was designed based on ACI 318-08 code including diagonal and spiral reinforcement, while the other specimens made with HPFRCC include, no spiral at the second specimen and no diagonal and spiral at the third specimen. Special instrumentation was used in the experimental specimens to measure the stain, displacement, and loads and rotations.The results showed that HPFRCC increased tensile capacity of concrete, prevented increasing the crack widths, increased absorbed energy and rigidity compared to plain concrete specimen; shear-tensile failure was changed to shear-slippage failure. Even though the spiral reinforcement was not used at the second HPFRCC specimen, the capacity and ductility were increased 20 and 37 percent respectively compared to the first specimen and casting the concrete was facilitated
EXPERIMENTAL EVALUATION OF HIGH-PERFORMANCE FIBER REINFORCED CEMENT COMPOSITES BEHAVIOR
No full textHigh-performance fiber cementitious composites are new materials in construction industry. Investigation into their behavioral characteristics needs experiments due to the lack of data. In this study, tensile, compressive and bending behavior of this material is examined using experimental tests.High-performance fiber reinforced cementitious composites (HPFRCC) have strain hardening response under straight tension after cracking. Numerous cracks are formed before the crack widening occurrence when these composites show hardening behavior. HPFRCC are basically integrated with two main components including fiber and mortar. These two ingredients are interactively affected due to interfacial bonding which develop a strong composite. The advantages of HPFRCC in comparison with normal and fiber reinforced concrete (FRC) are ductility, durability, and high-energy absorption capacity. In this paper, evaluation of strain hardening behavior in HPFRCC is conducted using straight tension and tensile strain-stress curve. Moreover, bending behavior, load-displacement curve, and toughness factor of this material are evaluated using four-point bending test, and the performance is compared with bending behavior of normal concrete. In these tests, three fiber types, including
hooped steel fiber, corrugated steel fiber, and poly propylene fiber, are used in the mortar separately and in combination with each other by volume percentage of 1.5\%. To achieve a proper strain hardening behavior, different mix ratios are investigated and the best mix design is determined. The results showed that all specimens mixed with fibers have strain hardening behavior accompanied by more cracks; consequently, the strength and strain of the HPFRCC specimens are increased significantly compared to those of normal concrete. The strength of HPFRCC specimens is between 5 to 8 times greater than that of normal concrete. In addition, the ultimate strains of the specimens are 70 to 100 times higher than that of normal concrete. Furthermore, toughness factor of HPFRCC specimens is 5 to 9 times higher than that of normal concrete. It is revealed that the mechanical properties of HPFRCCs have been considerably enhanced compared to normal concretes. HPFRCCs can be applied as an appropriate technique to restrain the reinforcement congestion, decrease the high value of transverse reinforcements at beam-column joints, and also improve the shear capacity and ductility of the members
EVALUATION DEMAND OF SEPARATION GAP ANGLE IN ADJACENT STEEL MOMENT RESISTING FRAMES UNDER FAR-FIELD AND NEAR-FIELD EARTHQUAKES
No full textIn crowded cities, building structures are usually constructed in close proximity to one another because of restricted availability of space. In many cases, every building in a block is in full or partial contact with its neighboring buildings. Because of insuf\u{fb01}cient separations, their different heights and seismic-resisting systems collision can occur between adjacent buildings during strong ground motions. This collision can make partial or general damages to the structural elements and accelerate their failure by affecting their stiffness. This phenomenon is commonly referred to as structural pounding. Pounding between inadequately separated buildings has been observed in most previous major earthquakes. Each time pounding occurs, building structures will sustain short duration large impact force not specifically considered in conventional designs. The severity of the impact depends on the dynamic characteristics of the adjacent buildings in combination with the earthquake characteristics. Aiming to prevent such collisions, the present study tends to estimate the demand of separation gap angle at the highest collision level using various proximity compositions of two regular
steel moment resisting frames under near-field and far-field earthquake records. Accordingly, 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 story three-span steel moment resisting frames are placed in all possible pair proximity states, and their demand of separation gap and separation gap angle is calculated using dynamic analysis of the nonlinear time history with the OPENSEES software, and compared to Standard 2800 (Fourth Edition) requirements. The results indicate that in some proximity states the Standard 2800 requirements underestimate the demand of separation gap angle. Meanwhile, the average of demand of separation gap angle in the states studied under the component vertical to the fault of near-field earthquakes is 1.48 and 1.35 times greater than those of the far-field earthquakes and the component parallel to the fault of near-field earthquakes respectively
Sensitivity analysis of the length of plastic hinge region in the flanged reinforced concrete shear walls
No full textPast earthquakes have shown that properly designed buildings using shear walls have great performance in dissipating a considerable amount of inelastic energy. It is notable that the reduction in seismic input energy occurs in plastic hinge area through inelastic deformation. Plastic hinge development in a RC shear wall in the areas with plastic behavior depends on the ground motions characteristics as well as shear wall details. One of the most generally used forms of structural walls is flanged RC wall. These types of shear walls have large in-plane and out-of-plane stiffnesses through flanges and can tolerate high shear stresses. Several international seismic design codes and guidelines have suggested special detailing to assure ductile response in this region. In this paper, the parameters that affect the length of plastic hinge region in the flanged RC walls were examined and the sensitivity of these parameters was evaluated with respect to the length of the plastic hinge region. Sensitivity analysis was conducted by independently variable parameters with one standard deviation away from their means. To this end, the Monte Carlo simulation, tornado diagram analysis, and first-order second moment method were employed to determine the uncertainties associated with analysis parameters. The results showed that among the considered design variables, the aspect ratio of the flanged RC wall (length to width ratio), length of flange to length of web (lf/lw), and axial load level were the most important design parameters in the plastic hinge region, while the yield strength of transverse reinforcements had the least effect on determining the length of this region
مرور مقایسه یی معتبرترین روش های برآورد رفتار درازمدت بتن تحت آنالیز متداول یک مرحله یی و آنالیز غیرخطی مرحله یی
No full textIn recent years, the need for consistency between the practical implementation steps of construction process and the design stage of high-rise concrete structure through the use of nonlinear sequential construction analysis has been strongly recommended by researchers. Besides, it is known by research and experiment that concrete structures are subjected to larger displacements and stresses because of the long-term behavior and the time-dependent parameters of concrete such as creep and shrinkage. This brings about the increase in beam deflections, expansion of tensile cracks in members, excessive column shortenings, differential displacements of horizontal structural members, such as beams, caused by unequal and increasing axial displacements in adjacent frame members and considerable redistribution of stress in structure. All these outcomes, which affect structure's response directly or indirectly, must be considered in the nonlinear and time-dependent sequential analysis of multi-story buildings. In this paper, the most important methods of predicting the long-term behavior of concrete, stating the advantages and disadvantages of each, has been introduced, and the proposed equations to describe the manner of applying certain features of the aforementioned methods in the updated version of the common analysis and design software for structures are presented. In addition, for getting familiar with the manual method of calculation of creep and shrinkage effects, the exact implementation of the Fintel and Khan's model
is expressed by establishing the tables of before and after the casting of concrete and considering the changes that illuminate the obscure aspects of the corresponding method. Proper compliance of the obtained results with the corresponding values of the similar method, named PCA, which has the finite-element modeling functionality, indicates the possibility of providing a reliable sample for error calibration and validation process. For vivid understanding of the effects of time-dependent parameters of the concrete on the axial deformation of the vertical elements of the structures, the invoked example of Fintel and khan has been applied similarly to all the studied methods under conventional one-step and nonlinear staged analyses. Moreover, the column shortening results have been compared after 1,000 days of construction time
EXPERIMENTAL STUDY OF MECHANICAL SPLICES OF TENSILE REINFORCED CONCRETE BEAMS UNDER BENDING
No full textIn order to investigate into the performance of mechanical splices, 6 RC beams
with the same dimensions and materials whose only difference is type and
location of splicing, have been tested. This study aims to assess the effect of
spacing between the splices with respect to their type. Indeed, the results of
this paper are intended to provide a proper understanding from location of
splices and its effect on the performance of the reinforced concrete (RC) beams. The results indicated that splices do not cause remarkable change in load-carrying capacity of the specimens. In addition, after applying loads and fracture of specimens, none of the mechanically-spliced rebars was ruptured at the location of splice and coupler remained undamaged. Further, it was observed that the reference beam and mechanically spliced beam (tension rebar in the mid-span and 2 other tension rebars with spacing of 60cm from mid-span and symmetrically distributed along the beam) exhibited minimum effective moment of inertia and thus, the same trend regarding flexural rigidity that is in direct relation to the moment of inertia, was attained. Accordingly, the reference beam and specimen L100 offered minimum displacement ductility. Specimen L33 and M33-60 exhibited 6\% increase and 10\% decrease in their strength respectively, experiencing maximum and minimum load-carrying capacity
Experimental and numerical investigation of an innovative buckling-restrained fuse under cyclic loading
No full textStructural fuses are sacrificial elements embedded in the structural members to localize potential failures within themselves. These replaceable segments are used to dissipate the energy of severe loads while preserving the integrity of the structure's major components. This paper presents an innovative Composite Buckling Restrained Fuse (CBRF) as a segment of a bracing element. CBRF with relatively small dimensions is a hysteretic damper with different performance in tension and compression. According to the typical difference of the bracing element capacities in tension and compression, the CBRF possess higher tensile strength than its compressive capacity. Utilizing tensile-only elements in this fuse with a new configuration improves the efficiency of the energy dissipation and eliminates the limitation of the tensile strength that exists in bracing members which contain ordinary ones. Key design parameters such as cross-sectional area and length of the fuse core are discussed theoretically. Six CBRF specimens with various dimensions and tensile-only elements were designed, tested and numerically modeled under cyclic loading to provide better insight into the fuse core and the encasing performance. The results indicated that the proposed structural fuse has a ductile behavior with maximum average core strain of 5.6% and sufficient tensile strength along with high energy absorption capacity
Performance of innovative composite buckling-restrained fuse for concentrically braced frames under cyclic loading
No full textConcentrically Braced Frames (CBFs) are commonly used in the construction of steel structures because of their ease of implementation, rigidity, low lateral displacement, and cost-effectiveness. However, the principal disadvantage of this kind of braced frame is the inability to provide deformation capacity (ductility) and buckling of bracing elements before yielding. This paper aims to present a novel Composite Buckling Restrained Fuse (CBRF) to be utilized as a bracing segment in concentrically braced frames that allows higher ductility and removes premature buckling. The proposed CBRF with relatively small dimensions is an enhancement on the Reduced Length Buckling Restrained Braces (RL-BRBs), consists of steel core and additional tensile elements embedded in a concrete encasement. Employing tensile elements in this composite fuse with a new configuration enhances the energy dissipation efficiency and removes the tensile strength limitations that exist in bracing elements that contain RL-BRBs. Here, the optimal length of the CBRF is computed by considering the anticipated strain demand and the low-cyclic fatigue life of the core under standard loading protocol. An experimental program is conducted to explore the seismic behavior of the suggested CBRF compare with an RL-BRB specimen under gradually increased cyclic loading. Moreover, Hysteretic responses of the specimens are evaluated to calculate the design parameters such as energy dissipation potential, strength adjustment factors, and equivalent viscous damping. The findings show that the suggested fuse possess a ductile behavior with high energy absorption and sufficient resistance and a reasonably stable hysteresis response under compression and tension
