Results Of Cyclic Loading Tests Research Articles

Experimental study on damage evolution process, seepage characteristics, and energy response of columnar jointed basalt under true triaxial cyclic loading

The physical response of Columnar Jointed Basalt (CJB) under a stress–seepage coupling field is of great significance for dam safety and oil and gas reservoir evaluation. A true triaxial experimental machine was used for investigating the deformation, damage evolution characteristics, seepage properties, and energy response of the CJB. Before the start of the test, a series of uniaxial compression tests were used to determine the ratio of similar materials, and the cyclic loading test results indicate that: The strength characteristics of CJB decreases slowly and then increases rapidly as the dip angle β varies from 0° to 90° under two loading conditions of the tiered cyclic loading (T–C) and the constant amplitude cyclic loading (CA–C), showing an obvious U–shaped trend, and four different loading stages can be distinguished by characteristic stress. In the yield stage, the stress–strain curve shows an obvious plastic hysteresis loop, there is a strong correlation between the failure modes of the CJB and β of the specimen, the joint surface gradually deteriorates owing to loading and unloading conditions, and structural control failure occurs widely in specimens. The damage evolution process is discussed in combination with the Load–Unloading Response Ratio, and the relative damage amount (Df) is defined by cycle index. The permeability–axial stress relationship of the specimen conforms to the power exponential relationship, and the permeability evolution characteristics are strongly correlated with the degree of damage. The energy response of the CJB were investigated by tress–strain curve, under two loading modes, T–C and CA–C, the cumulative curves of dissipation energy Ed can be fitted by an exponential function and a logarithmic function, respectively. The findings of this research hold immense importance for clarifying the mechanical and seepage properties of CJB under a stress–seepage coupling field.

Lateral hysteretic behavior of precast concrete shear walls with unjointed vertical distribution bars and opening

Precast concrete shear walls with unjointed vertical distribution bars have desirable lateral resistance compared with cast in situ concrete shear walls and much less construction cost as no sleeve splicing joint is needed. However, the influence of opening in the precast panels on their lateral hysteretic behavior has not been fully investigated. This study presents the results of cyclic loading tests of three full size precast concrete shear walls with unjointed vertical bars and opening. The test results showed that these shear walls had similar failure modes as a cast in situ concrete shear wall, such as cracking in the corners of the opening and the concrete and steel bars crushing at the bottom corners of the shear walls. The peak load of the positive and negative loading cycles and the stiffness of the unjointed shear wall with a window opening were 14.6%, 4.3% and 1.3%, respectively, smaller and the ductility ratio was 37.6% higher, than an otherwise the same cast in situ shear wall. The lateral stiffness of the unjointed shear wall with a door opening was 35% smaller than that of the one with a window opening, due to the stiffness contribution of the wall segment underneath the window opening. The development of the longitudinal strains of concrete and steel strain along the height of the wall limbs generally met the plane section assumption. However, those next to the vertical joint interface were affected by the development length of the shear force after the bedding mortar cracked under tension. The determination of the development length needs to consider the influence of the stiffness of the link beam and the wall segment underneath the opening.

EXPERIMENTAL STUDY ON THE STRUCTURAL BEHAVIOUR OF RECYCLED PLASTIC ONE STORY HOUSES

Recycling plastic materials may constitute a relief measure to the global plastic problem. Several companies are now producing recycled plastic for use as construction material in single-story houses. One commercially available layout involves assembling Recycled Plastic Lumber units in a running bond pattern, forming panels confined by horizontal and vertical tie elements joined through bolted steel plate connections. As production of houses is industrialized, the architectural layouts are standardized according to specific distribution and dimensions. This paper presents the findings of an experimental program aimed to characterize the seismic behavior and properties of a one-story house model. To facilitate practical application, the model is referred here as Architectural Standard Model (ASM). The objectives of the test campaign were to investigate the structural behavior of the constituting members and assemblies, and the response of structural walls to cyclic static lateral loads. Three natural scale wall specimens were tested in-plane and two out of plane. Results of natural scale cyclic loading tests demonstrated that structural system of the ASM can perform acceptably safely under high seismic loads if it is adequately fixed to the foundation. The results showed that out of plane loading was the critical pattern and behaved like a unidirectional plate that transmitted load to the columns. In plane observed behavior exhibited predominating rocking component, which suggests considering an evaluation of the system's response using dynamic methods.

Concrete reinforcement using composite fiberglass-based materials

Numerous existing structures, both old and new, have serious load-bearing capacity issues, which, in some cases, could endanger the safety of their users. In fact, we can say that these structures are nearing (or have already reached) the end of their useful lives, necessitating the need to find technical and financial solutions to renovate them as efficiently as possible. Many reinforced concrete bridges experience advanced states of deterioration as a result of extended exposure to hostile environments or even continuously rising use loads. Additionally, since the time of their construction, the technical standards used for the design and dimensioning of the old structures have had to be updated. As a result, some structural components that are still in use do not adhere to the standards for response to loads. In fact, it is frequently less expensive to reinforce the structural components of buildings than to perform a full reconstruction, especially now that, thanks to technological advancements, a variety of reinforcement techniques are still available and their costs are decreasing. One such technique involves externally reinforcing reinforced concrete elements with composite materials because of their superior strength-to-weight ratio and resistance to abrasion. Additionally, these composite materials can be utilized for column containment as well as shear and bending reinforcement for beams. This study aims to evaluate the impact of glass fibers on the general behavior of concrete, in particular on its resistance, deformations, and ductility, using FRP: Fiber-reinforced plastics are materials generally formed of two main and distinct elements: the fiber, "made from glass," and the matrix, "an epoxy resin that allows the transfer of loads between the fibers. The results of the specimens' cyclic loading tests attest to the significance of the contribution that concrete specimen confinement with FRP can make in terms of deformation and resistance to compression after the completion of static loading tests. However, these tests on the specimens' ability to withstand loading and unloading cycles reveal a very significant improvement.

A Novel Method to Predict Shaft and Base Responses of a Pile from Cyclic Pile Load Test Results

A Novel Method to Predict Shaft and Base Responses of a Pile from Cyclic Pile Load Test Results

A Systematic Study to Strengthen the Sub Grade of the Pavement by Stabilization of Expansive Soil with Molasses and Jute Fibre

Abstract: Expansive soils, commonly referred to as Black cotton soils (BC), possess undesirable engineering properties such as low bearing capacity and high compressibility. To address these challenges, various stabilizers have been used to enhance the strength of expansive soil, including jute fiber and molasses. This thesis focuses on investigating the effects of incorporating jute fiber as a stabilizer and molasses as an additive to improve the properties of expansive soil. The objectives of this study are to enhance the shear strength of expansive soil by blending jute fiber and molasses mixtures. Jute fibers of different lengths (1cm, 2cm, 3cm, and 4cm) and various percentages (0.5%, 1%, 1.5%, and 2%) are used as stabilizers. Molasses is employed as an additional stabilizer with varying percentages (5%, 8%, 12%, and 15%). Laboratory investigations reveal that the addition of 12% molasses and 1.5% jute fiber significantly reduces the liquid limit, plastic limit, and plasticity index of the expansive soil, while simultaneously increasing the maximum dry density and California Bearing Ratio (CBR). Furthermore, cyclic load test results demonstrate a 62% improvement in the load carrying capacity of the treated expansive soil subgrade flexible pavement compared to untreated expansive soil flexible pavement. Utilizing construction wastes like molasses offers an alternative to reduce road construction costs, especially in rural areas of developing countries. Additionally, jute fiber provides effective reinforcement for expansive soils. These findings highlight the potential of jute fiber and molasses as sustainable and cost-effective stabilizers for enhancing the performance of expansive soils in construction projects

Seismic performance of L-shaped short-leg shear walls with different concealed support materials

This paper reports a study of the effects of different concealed bracing materials on the seismic performance of short-legged shear walls and presents the results of low-frequency cyclic loading tests on three L-shaped short-leg shear walls—one wall without concealed bracing and the other two with concealed bracing materials of steel bars and SMA bars, respectively. The tests were aimed mainly at analyzing the effects of different concealed bracing materials on seismic performance indicators such as crack pattern, bearing capacity, ductility, hysteresis performance, stiffness, and energy dissipation of the L-shaped short-leg shear walls. The results revealed that their seismic performance with concealed bracing was better than without concealed bracing. The short-leg shear walls with SMA bar concealed bracing had the lowest number of cracks and the smallest crack width, and the effect of delaying the development of cracks was more evident. The short-leg shear walls with steel reinforcement and SMA-bar concealed bracing were better in bearing capacity, ductility, and energy dissipation capacity, with, respectively, 11% and 26.3% increase in ultimate load, 4% and 18.6% increase in ultimate displacement, and 12% and 28% increase in energy dissipation. It can be seen that setting concealed bracing effectively enhances the seismic performance of short-leg shear walls, and that short-leg shear walls with concealed SMA bar bracing have the most significant improvement in seismic performance.

Experimental evaluation on the seismic performance of high-strength reinforcement beam-column joints with different parameters

This paper reports the results of cyclic load tests and analysis of full-scale beam-column joints using 600 MPa high-strength reinforcement as beam longitudinal reinforcements. The focus was on evaluating the effect of the relative length of beam bars through the joint (hc/d) on the seismic performance of the high-strength reinforcement beam-column joints, while the effects of variables such as axial compression ratio, shear compression ratio, and transverse reinforcement ratio were also discussed. The failure pattern, strength, stiffness, ductility, energy dissipation, and bond performance of each specimen under reciprocal loading were analyzed. The test results showed that applying high-strength steel bars improved the failure pattern, load-bearing capacity, and energy dissipation of the joints. The increase in hc/d improved the bond degradation of the high-strength reinforcement, which positively influenced the seismic performance of the joint. Conversely, high axial compression ratios and high shear compression ratios had a clear negative effect on the bond degradation and failure patterns when high-strength reinforcement used. A proposed equation for adjusting the hc/d in a high-strength reinforcement joint was also presented, which considered the effect of concrete strength and reinforcement strength on the bond performance of beam reinforcement.

Experimental investigation on the behavior of grouted restrained anchor connections for cluster-reinforced precast concrete columns

Quality, safety, and construction efficiency of assembled buildings are closely related to the connection between precast components. However, the traditional connection technique requires a high number of reinforcing bars, resulting in inefficient installation. The present paper proposes using a bundle of small-diameter reinforcing steel bars instead of multiple bars or larger bars arranged in the column. Therefore, the connection number of vertical steel bars is reduced, and the anchorage length of steel bars in the precast member is shortened so that the assembly is simplified and installation efficiency is enhanced. This paper also presents the results of cyclic loading tests and finite element analyses on precast concrete columns with semi-grouted and full-grouted restrained clustered bars. The purpose is to investigate the effects of anchorage length and tensile strength of vertical steel bars, axial compression ratio, and other parameters on connection performance to ensure adequate structural performance. It was found that both the full-grouted and semi-grouted restrained connection of tensile steel bars can transfer stress effectively. It will be also shown that these connection methods of vertical steel bars are suitable for precast concrete columns.

Restoring force characteristic model for bending moment–rotation angle relationship of concrete‐filled square steel tube beam‐columns

AbstractThis paper proposes a new simplified restoring force characteristic model of the bending moment–rotation angle relationship for square concrete‐filled steel tube (CFT) beam‐columns to estimate the elastoplastic flexural‐shear behavior from short to slender beam‐columns. The square CFT beam‐column model incorporates a reduction in strength after the ultimate strength. The proposed simplified model is multilinear and involves a cracking strength point, a yield strength point, an ultimate strength point, and strength reduction points. In the proposed model, each flexural strength is calculated by a general superposed strength method, and new empirical expressions for each rotation angle are proposed from the results of previous experimental cyclic and monotonic loading tests. The proposed model for the bending moment–rotation angle relation is found to agree approximately with experimental results up to large rotation angles.

Seismic Response of GFRP-RC Interior Beam-to-Column Joints under Cyclic Static Loads

A total of nine specimens were constructed and tested under cyclic loads to investigate the differences in seismic behavior between glass fiber-reinforced polymer (GFRP)-reinforced concrete (RC) joints and RC beam-to-column joints. The experimental parameters included stirrup ratios, axial pressure ratios and concrete strength of the beam-to-column joints. The cyclic loading test results showed that the GFRP-RC beam-to-column joints can withstand significantly high lateral deformations without exhibiting brittle failure. Moreover, the RC beam-to-column joint exhibited significantly higher energy dissipation and residual displacement than the GFRP-RC beam-to-column joint by 50% and 60%, respectively. Finally, a shear capacity calculation method for the core zone of this kind of joint was proposed, which agreed well with the experimental results.

Seismic application of steel rocking column bases with replaceable cover plates in steel MRFs

This paper presented unidirectional and bidirectional cyclic loading test results of a novel steel rocking column base. Feasibility of the column base in steel moment-resisting frames was verified through nonlinear static and time history analysis. It was found that the column base was capable of dissipating seismic energy through plastic bending deformation of the replaceable cover plates and flag-shaped hysteretic curves can be observed. Nevertheless, it is not expected to provide much energy dissipation for the whole structural system, since the plastic bending deformation of each cover plate is only in one direction. A three-dimensional simplified numerical model of the column base was developed and validated against the test results. Following that, nonlinear static and time-history analysis were conducted on prototype steel moment-resisting frames with and without the rocking column bases. In general, replacing some column bases with the rocking ones (i.e., 4/24 of all in this study) did not cause much reduction in lateral resisting stiffness and capacity. Moreover, this reduction was even slighter when the loading direction was perpendicular to the weak axis of the rocking column section. On the other hand, replacing all fixed column base with the proposed rocking column base may cause drift concentration in the ground storey, which is too radical for the prototype building. The seismic responses of modified frames were generally very close to that of the original frame with all fixed column bases. Even though the maximum drifts in the ground storey of these frames were larger than that of the original frames with fixed bases, the maximum drifts of the whole structures were not expected to be amplified. • Bidirectional cyclic loading tests on a novel steel rocking column base were conducted. • The column base showed flag-shaped hysteretic cures and dissipated seismic energy through plastic deformation of the replaceable cover plates. • Feasibility of the column base in steel moment-resisting frames was verified through nonlinear static and time history analysis. • Replacing some column bases with the rocking ones did not cause much reduction in lateral stiffness and capacity.

Behavior of deformation joints of RC utility tunnels considering multi-hazard conditions

Utility tunnels have been widely constructed worldwide to accommodate the lifeline infrastructure and ever-expanding municipal needs caused by fast population concentration and urbanization in recent years. Typical reinforced concrete utility tunnels consist of tunnel segments no longer than 30 m in length and deformation joints between adjacent segments. Although extensive research has been carried out on the seismic behavior of utility tunnels using shaking table testing and numerical method, little progress has been made in the understanding of the mechanical behavior of deformation joints under differential settlement and earthquake ground motion. Engineering practice has demonstrated that the deformation joints also play an important role in ensuring the functionability and durability of utility tunnels. In this research program, two groups of eight test models of utility tunnel deformation joints with shear dowel bars were constructed and tested under monotonic and reversed cyclic loading respectively, aiming to simulate the responses of the deformation joints subjected to differential settlement and earthquake excitation. Both ends of each shear dowel bar were inserted into adjacent segments for certain length, where one end is bonded with the segment concrete while the other debonded to allow for potential longitudinal movement due to temperature change. Concrete strength, dowel bar amount, insert length and layout were considered as the test variables. Test results indicated that concrete strength has little influence on the shear capacity of deformation joints. Placing dowel bars only at two vertical sides of the tunnel box-section can improve the deformation capacity and avoid concrete cracking at the bottom slab of the deformation joints. The reversed cyclic loading test results showed great seismic performance of the test models with great load bearing capacity, ductility, energy dissipation and stiffness. Although arranging all dowel bars at side walls can reduce the cracking of bottom slabs, the ductility and energy dissipation capacity are less favorable compared with placing dowel bars all around the box-section. In addition, although 10d is sufficient for the dowel bar insert length, it is suggested that use of 15d can help prevent severe concrete damages. The numerical analysis verified the test results and can be used for further study of the deformation joints of utility tunnels.

Experimental Study on Sealing Failure Mechanism of Injection-Production String in Underground Gas Storage under Cyclic Loading

In order to clarify the impact of cyclic loading on the mechanical properties and sealing performance of threaded connections on pipe string under the injection-production conditions of gas storage and the airtight threaded connections suitable for the actual working conditions can be preferred, the sealing failure of injection and production tubular strings of several domestic gas storages was investigated comprehensively. It was found that the airtight threaded connections with different performance may leak during the service of tubular strings. Existing standards and testing methods have limitations, which are not fully applicable to the working environment of gas storage wells and the production mode of forced injection-production and cannot reflect the operation characteristics of multiround injection and production. Based on the stress analysis of the tubular string during injection and production, a full-scale simulation testing of 30 cycles of gas seal cycle under alternating load was proposed. The cyclic loading test results of two P110·13Cr tubing in domestic gas storage showed that after 30 cycles of cyclic loading, the yield strength, internal pressure strength, collapse strength, and compressive bearing capacity of tubing were all decreased; the compression efficiency of the joints should be fully considered when selecting the gas-sealed thread.

Post-earthquake fire performance of fire door sets

This paper presents the results of an experimental cyclic and fire test program to investigate the fire performance of fire door sets after experiencing simulated earthquake damage. The earthquake damage mimics that of a 35-story tall residential benchmark building subject to design earthquake intensity level, inducing an inter-story drift of 57 mm. Three earthquake-damaged 90-min rated fire door sets were subject to displacement controlled quasi-static cyclic loading test at ambient temperature and then to standard fire resistance tests. Results of cyclic load tests at ambient temperature reveal severe distortion of the fire door frames and excessive gaps, notably at top corners. Results of the subsequent standard fire resistance tests show that the fire resistance of the damaged fire door sets decreased by as much as 70%. The reduction can be attributed to large gaps due to the distorted door geometry after seismic loading, substantial loosening of the door hinges and damaged intumescent seals around the door. Maximum gap measurement of 8 mm between the door and door frame is considered as the threshold above which the fire compartment is compromised, and fire door set replacement is necessary.

Seismic Retrofitting Method Using CFRP Sheets for H-Section Steel Beam with Variable Cross Section

Severe damage to steel bridge piers and steel rigid-frame piers starting from regions of abrupt change in cross section has been widely reported. Therefore, finding a simple and effective seismic retrofitting method for steel structural members with variable cross sections to improve their plastic deformation performance is currently an urgent concern. The objective of this study was to establish an effective seismic retrofitting method for H-section steel beams with abruptly variable cross sections using a carbon fiber–reinforced plastic (CFRP) sheet because of its outstanding properties such as light weight, high strength, and superior durability. Bending and bending-shear cyclic loading tests were conducted with two parameters, including the type of CFRP sheets, and whether or not polyurea putty was inserted between the CFRP sheet and steel beam. The test results indicate that the proposed retrofitting method using intermediate-modulus CFRP and polyurea putty increases the load-carrying capacity, ductility, energy dissipation capacity, and bending stiffness of H-section steel beams significantly without any failure. Further, by implementing finite-element (FE) analyses considering the actual cyclic plasticity properties of steel, anisotropic performance of the CFRP sheets, and nonlinear bond-slip properties of the polyurea putty layer, the cyclic loading test results were reproduced accurately. Moreover, in the cases in which the polyurea putty was applied, parametric FE analysis of the CFRP bonding method with and without creating a stepped length at the top of each CFRP sheet showed that the retrofitting method without the stepped length was similar in effectiveness to the method with the stepped length.

Improving brace member seismic performance with amplified-deformation lever-armed dampers

This study focused on the development and validation of a novel brace design that incorporated a hinged truss member and a set of lever-armed damper (LAD), namely LAD-Brace, for structural performance enhancement. The lever-armed damper was designed with adequate rotation mechanism to generate amplified-deformation and uniform yield zones in the tapered energy dissipation plate for efficient energy dissipation. A series of cyclic loads and constant peak amplitude tests were conducted on LAD-Braces with various geometries in the energy dissipation plates. Analytical expressions for yield strength estimation were derived and effectively validated by the test results. Cyclic load test results showed that adequate strength, effective equivalent viscous damping and significant energy dissipation were simultaneously achieved which justified the design applicability for earthquake-resistant purposes. Investigation through constant peak amplitude tests revealed that LAD-Braces, when designed with adequate geometries, possessed further seismic resilience after experiencing major earthquake excitation, thus validated the proposed design effectiveness and robustness.

A Simplified Ductile Fracture Model for Predicting Ultra-Low Cycle Fatigue of Structural Steels.

Under strong earthquakes, steel structures are prone to undergoing ultra-low cycle fatigue (ULCF) fracture after sustaining cyclic large-strain loading, leading to severe earthquake-induced damage. Thus, establishing a prediction method for ULCF plays a significant role in the seismic design of steel structures. However, a simple and feasible model for predicting the ULCF life of steel structures has not been recognized yet. Among existing models, the ductile fracture model based on ductility capacity consumption has the advantage of strong adaptability, while the loading history effect in the damage process can also be considered. Nevertheless, such models have too many parameters and are inconvenient for calibration and application. To this end, focusing on the prediction methods for ULCF damage in steel structures, with the fragile parts being in moderate and high stress triaxiality, this paper proposes a simplified uncoupled prediction model that considers the effect of stress triaxiality on damage and introduces a new historical-effect related variable function reducing the calibration work of model parameters. Finally, cyclic loading test results of circular notched specimens verify that the proposed model has the advantages of a small dispersion of parameters for calibration, being handy for application, and possessing reliable results, providing a prediction method for ULCF damage of structural steels.

Assembled self-centering energy dissipation braces and a force method-based model

A pre-pressed spring self-centering energy dissipation (PS-SCED) bracing system has significant energy dissipation and re-centering abilities, although many welds result in a lengthy manufacturing process and reduce the machining accuracy to an unacceptable level. An assembled pre-pressed spring self-centering energy dissipation (A-PS-SCED) bracing system that uses disc spring groups to provide a re-centering ability and a friction device to dissipate energy, is presented in this paper to simplify production and maintenance. A novel force method-based (FMB) hysteretic analysis model governing the distribution of the internal force is proposed and verified by a numerical model of the A-PS-SCED brace and tests of the PS-SCED brace specimen. The simulation results indicate that the A-PS-SCED brace exhibits sufficient and steady energy dissipation and re-centering capacities. The FMB model agrees well with the numerical model with a maximum bearing force difference of 2% and has steady hysteretic responses under random excitations. The FMB model is used to determine the mechanisms of the stiffness and contact status change during a typical loading process. Additionally, the FMB model accurately predicts the cyclic loading test results of an existing PS-SCED brace specimen, and the average bearing force differences are 6% and 2% at friction force of 200 kN and 300 kN, respectively.

Lateral force-displacement response of rat-trap bonded masonry

Rat-trap bond (RTB) masonry is one of the most economical, fast, and energy efficient construction technique for brick masonry buildings. Many developing countries including India, Nepal, Sri Lanka and Pakistan have constructed large number of buildings using this technique. However, structural stability and performance validation are as important as the economy in any construction project. Therefore, this study presents the results of in-plane quasi-static cyclic load tests on three wall specimens constructed in RTB. The pre-compression load was adjusted to simulate the load condition of a typical two storey building. The key parameters evaluated include stiffness, ductility, damping, energy dissipation, force-displacement behaviour, lateral strength, etc. The experimentally obtained results were also compared with the existing research of similar nature on conventional masonry as well as with the results predicted by various empirical equations. The comparison indicates that the lateral strength and stiffness of rat-trap masonry is significantly less than those of conventional masonry because of the reduced effective thickness, while other properties like ductility, damping and energy dissipation do not show any significant variation.