Residual Shear Capacity Research Articles

Shear behavior of reinforced concrete beams with high-strength reinforcements after high temperatures

This paper investigates the effect of steel reinforcement configured with different strengths after different high temperatures on the shear performance of the test beams, a total of 20 reinforced concrete (RC) beams, through experiments, numerical analyses and theoretical studies, in order to understand the key factors affecting the shear performance of the beams. The test revealed that the mechanical properties of concrete and steel reinforcement showed a trend of increasing and then decreasing after high temperatures. Increasing the stirrup ratio and stirrup strength can significantly improve the crack resistance and shear capacity of the beams, as well as the deformation performance of the beams. The residual shear strengths of test beams with high-strength stirrups after exposure to high temperatures are significantly greater than those of ordinary reinforced concrete beams. Specifically, the shear capacity of beams with high-strength stirrups after exposure to 800°C increased by 23.7 % compared to ordinary beams, and the mid-span deflection performance increased by 28.7 %. The stresses in the shear span region of the test beams after high temperature were more concentrated at the diagonal and the number of cracks was significantly reduced. In this paper, a simplified formula for calculating the residual shear capacity of RC beams after room and high temperatures is proposed, which can well predict the test results.

Experimental and theoretical study on the shear behaviors of an innovative precast UHPC composite beams reinforced with inverted T-shaped steel

The innovative precast composite beam consisted of reinforced UHPC beam and inner inverted T-steel shape (forming ITSRU composite beam) is proposed for the marine structures serviced in harsh environment and subjected to complicated loading conditions. The novel composite beam possesses the advantages of lightweight, high strength and ductility, enhanced durability. To study the shear behaviors of ITSRU beams, a shear test program consisted of seven composite beams were conducted to study the effects of shear span-to-depth ratio, steel fiber volume fraction, stirrup ratio and inverted T-steel web thickness. UHPC used in this paper possess compressive strength more than 125 MPa, ultimate tensile strength more than 8.9 MPa and ultimate tensile strain more than 2256με. The inverted T-steel and steel rebar used in this paper have grades of Q355 and HRB400, respectively. A segmented loading control method was used in the shear test, in which a forced-controlled with a rate of 20 kN/min was used before the beam yield and the displacement control was implemented at a rate of 0.5 mm/min after reaching the yield load. The test results revealed that the ITSRU beams exhibited admirable deformation capacity and considerable residual shear capacity even for the composite beam with shear span-to-depth ratio of 1.0. The increasing of stirrup ratio, steel fiber volume fraction and inverted T-steel web thickness could improve the shear resistance and the ductility as well as suppress the appearance of the diagonal shear critical cracks. Based on the test results, an analytical shear model considering the contributions of UHPC in shear compression region, stirrups, steel fibers and inverted steel web was developed to predicted the shear resistance of ITSRU beams. The interaction mechanism of the different components in the ITSRU beams was considered in the analytical shear model. The accuracy of the developed calculation method was verified by the test results.

The importance and use of vertical crack displacements for the assessment of existing reinforced concrete deep beams

The accurate assessment of cracked reinforced concrete structures is becoming increasingly more important as the world’s infrastructure ages and resources for retrofit and replacement remain limited. While existing approaches can be used to predict crack information for comparisons with on-site observations, there remains a need to establish methods that use crack measurements as a direct input to assess residual structural capacity. Critical wide cracks have been observed in lightly reinforced deep beams leading to questions about the safety of concrete bridges. To assess such deep members, this paper answers three important questions: 1) which critical crack displacements should be measured?; 2) where should the critical crack displacements be measured?; and 3) what is the residual shear capacity of the member, given the measured critical crack displacements? To answer these questions, detailed data from large-scale experiments is examined and interpreted with the two-parameter kinematic theory (2PKT). The results illustrate the importance of vertical crack displacements for conducting assessments of lightly reinforced deep beams. The paper shows that when the measured crack shape is incorporated into the 2PKT, the residual capacity of deep beams can be determined from measured critical crack displacements.

Finite Element Analysis of the Shear Capacity of Recycled Aggregate Concrete Beams with Corroded Stirrups

In this paper, a model to predict the residual shear capacity of RAC beams with corroded stirrups was established, and the simulation analysis was conducted on recycled concrete beams with different corrosion level using ANSYS. The reliability of the finite element analysis model was verified by comparing the finite element results with experimental results.

Residual Shear Capacity of Post-Fire RC Beams under Indirect Loading

Building fire is one of the most frequent disasters. The mechanical properties of concrete and steel will deteriorate to different degrees under fire exposure, thus weakening the bearing capacity of reinforced concrete (RC) members. Therefore, it is of great theoretical and practical significance to carry out research on the bearing capacity of RC members subjected to fire. To study the residual shear capacity of post-fire RC beams under indirect loading, static load tests were carried out on six full-scale RC beams to investigate the development of diagonal cracks and failure modes under an indirect load. Numerical models were established with ABAQUS to study the effect of the shear span-to-depth ratio and stirrup ratio on the residual shear capacity of the tested beams after fire exposure, and the shear capacity calculation method of indirectly loaded beams after high temperature is proposed. The results indicate that although the fire had no obvious affect on the failure mode of the beam under indirect loading, the fire aggravated the failure degree of the beams without additional transverse reinforcement. Moreover, the ultimate bending capacity of beams with additional transverse reinforcement decreased obviously after fire. The residual shear capacity of indirectly-loaded beams subjected to fire decreased compared with the directly-loaded beams due to the variation in the shear span-to-depth ratio and stirrup ratio. The shear capacity theoretical calculation results of the indirectly-loaded beam after high temperature were in good agreement with the tested results, and the average absolute error was 3.88%. Therefore, this calculation method for an indirectly loaded beam with a shear span-to-depth ratio less than 3.0 after fire as proposed in this paper was effective. The findings of this study are expected to provide a reference for the improved fire-resistant design of RC structures under indirect loading.

Post-buckling shear capacity of the corroded end panels of H-shaped steel beams

The shear capacity of steel beams can be affected by corrosion when the effective thickness is reduced. However, the contribution to shear capacity of beams with corroded steel web from support stiffener and flange has not been quantified until now. Thus, this work aims to reveal the changing rules of the shear capacity of randomly corroded steel beam while considering the nonlinear buckling behavior of the corroded web. The established numerical model is first validated through code-based semi analytical results. The contribution from support stiffener and flange are then investigated in detail. The influences of corrosion location, corroded thickness, thickness of support stiffener or flange, corrosion size, and corrosion severity on the reduction of shear capacity are investigated. Both the constant and random corroded depths are considered. The results show that the shear capacity corresponding to local corrosion is lower than uniform corrosion. This is caused by the corrosion located at different positions, which can influence the shear capacity in varying degree. Furthermore, the diameter of the corrosion pit has no influence on residual shear capacity and can be taken as a constant value. The influence of corrosion parameters on reduction factor is also quantified. The conclusions derived in this work can be directly applied to steel beams under actual conditions.

Residual Shear Capacity of RC Beams without Stirrups after Fire Exposure

To investigate the shear capacity and failure mechanism of RC beams after fire exposure, fourteen full-scale beams without stirrups were tested at ambient temperature and after fire exposure. Three parameters, including the loading ratio, shear span-to-depth ratio and longitudinal reinforcement ratio, were considered in static load tests. The deterioration mechanism of the shear bearing capacity at the diagonal section of RC beams without stirrups after fire exposure was experimentally, numerically and theoretically revealed, and a calculation formula for the shear capacity of post-fire beams without stirrups was proposed. The results show that the shear capacity and stiffness of the specimens decreased after fire exposure, and the shear strength loss of the beams increased with fire exposure time. The shear capacity and stiffness of fire-damaged specimens decreased as the shear span ratio λ increased, and the shear strength loss of the beams decreased with λ. Compared with the theoretical calculation and experimental results of beams without stirrups, the average of the absolute errors was 10.48%. Therefore, this formula can better calculate the residual shear capacity of beam without stirrups after fire exposure.

Three-dimensional failure envelope of concrete dam shear keys

Shear keys provide interlocking mechanisms along the vertical contraction joints of many concrete gravity dams. The shear key ultimate shear capacity is typically estimated as a function of the friction and cohesion that could be mobilised across a 2D shear plane located at the base of the key when subjected to a normal confinement pressure, P. A two-dimensional response of dam monoliths and shear keys shearing-off at their bases, is assumed. However, evidence of 3D interlocking behaviour between dam monoliths and the possibility of different key failure mechanisms involving interacting axial, P, shear, V, moment, M, and torsion, T, indicates that typical empirical formulations could significantly overestimate the actual shear key capacity under floods and seismic loadings. This paper presents an evaluation of the load–displacement response of shear keys subjected to multiaxial loading via nonlinear finite element analyses. A concrete “Continuous Surface Cap Model” (CSCM), available in the computer program LS-Dyna, is first shown to best capture the experimental shear keys' ultimate and residual shear capacity responses among five constitutive models. The effects of the tensile strength, fracture energy, confinement pressure, friction coefficient, initial opening, and dilation conditions on the load–displacement response of keys are investigated. Failure envelopes considering the key multiaxial shear capacity with confinement pressure, P, moment, M, and torsion, T, are developed. The ratios between moment and shear, M/V, and torsion and shear, T/V, control the failure mechanism. Increasing these ratios significantly reduce the ultimate shear capacity.

A machine‐learning‐based constitutive bond‐slip model for anchored CFRP strips externally bonded on concrete members

AbstractStrengthening is often required for reinforced concrete, steel, and masonry structures or structural elements when they possess insufficient performance against external loads such as earthquakes. Recently, the use of carbon fiber‐reinforced polymers (CFRP) has been considered a viable strengthening technique alternative to traditional methods. The major concern is premature debonding failure hindering the efficient use of CFRP systems. FRP anchor systems have been used to avoid this phenomenon. This paper employs a machine learning (ML)‐based algorithm (support vector regression) to propose predictive models to simulate the bond‐slip behavior of anchored CFRP strips externally bonded to the concrete surface. A comprehensive database was constructed using the previous reports on the bond‐slip behavior of FRP‐to‐concrete joints anchored with CFRP strips. Afterwards, the collected database was used to train and validate the proposed models. The input parameters cover all possible factors, that is, compressive strength of concrete, width of concrete block, anchor hole diameter, anchor hole depth, number of anchors at one row, number of anchors at one column; elastic modulus, width, bonding length, and thickness of CFRP strip. The output parameters are maximum shear capacity, residual shear capacity, displacement values at peak shear, and residual shear. Results imply that the proposed models have high prediction accuracies with low error rates. Proposed models are also presented in code format to be easily incorporated into analysis software for practical use.

Experimental study on shear behavior of joints in precast concrete segmental bridges

A new shear key was designed in precast segmental bridges, and 12 full-scale specimens were carried out. The types of shear keys (concrete key, steel shear key, inserted reinforcement key), joint types (dry, epoxied), and the number of shear keys (single-key, double-key represented multi-key) were taken as experimental parameters to study the crack development, failure mode, shear slip, ultimate shear capacity, and residual shear capacity of various joints under direct shear loading. The results showed that the stiffness and shear capacity of the steel shear keyed joints are higher than the concrete keyed joints, and the horizontal prestressed system is more stable than the concrete keyed joints at the moment of cracking. There is a local compressive stress concentration in the inserted reinforcement keyed joint, and the load–displacement curve has a long development course, resulting in the large shear slip when the specimen is damaged, which is not suitable as a shear key. The shear slips of steel shear keyed joints are smaller than the concrete keyed joints and inserted reinforcement keyed joints, just are 0.02 ∼ 0.03 mm. The shear capacity of the double-key is 46.66% higher than that of the single-key of steel shear key dry joint. The shear capacity of steel shear key epoxied joints is increased by 69.68%∼118.33% compared with the dry joints. The steel shear key epoxied joints are a direct shear failure, but the mechanical property is similar to the dry joints after direct shear failure, and the ratio of residual shear capacity to ultimate shear capacity is large. Steel shear key has obvious advantages based on mechanical property, simple manufacture, and convenient construction.

Experimental study on the effect of column lateral friction torque on seismic performance of IMS structure middle joints

The design of prestressed friction joints of integral prestressed prefabricated frame structure system (IMS) has a direct impact on the internal force distribution and deformation of the structure. To study the seismic performance of the IMS structure under low cyclic reciprocating load, quasi-static tests were carried out, and two spatial two-way prestressed frame beam slab column middle joints were designed. The effects of friction torque produced by lateral prestress on the ultimate bearing capacity, stiffness degradation, energy dissipation performance, and self-centering of joints are compared and analyzed. The test results show that the specimen SCJ2 with large column lateral friction torque is better than the specimen SCJ1 in initial stiffness, bearing capacity, and energy dissipation, but the self-centering ability and damage control are slightly poor; The column lateral friction torque is about 31.64% of the cracking moment of joint SCJ1, 7.51% of the ultimate moment, 43.58% of the cracking moment of joint SCJ2, and 10.99% of the ultimate moment, the column lateral friction torque has a great impact on the crack resistance and bearing capacity of the joint, which can not be ignored in the design. At the same time, to verify the safety of the prestressed friction joint of the IMS system and evaluate the friction and shear performance of the joint after a large earthquake, the residual shear capacity of the joint is tested on the specimens after the quasi-static test. The test results show that IMS prestressed friction joints can still ensure good shear performance and have sufficient reserve of post-earthquake shear capacity.

Shear behavior of steel reinforced recycled aggregate concrete beams after exposure to elevated temperatures

This paper experimentally investigates the shear behavior of steel reinforced recycled aggregate concrete (SRRAC) beams after exposure to elevated temperatures. A total of seventeen specimens, including thirteen SRRAC beams exposed to elevated temperatures (i.e., 200 °C, 400 °C and 600 °C) and four SRRAC beams at room temperature as reference, were fabricated with different recycled coarse aggregate (RCA) replacement ratios of 0, 30%, 70% and 100%, respectively. The influence of different parameters (i.e., temperature, RCA replacement ratio and compressive strength of concrete) on the shear behavior of SRRAC beams was investigated intensively. The experimental results indicate that the concrete colour changes from light grey to grayish-reddish with increasing temperature. Increasing temperature and RCA replacement ratio can increase the weight loss of SRRAC beams. The failure patterns of SRRAC beams are similar to those of steel reinforced natural aggregate concrete (SRNAC) beams after exposure to the same elevated temperatures, and the bearing capacity and initial stiffness of beams will reduce as the temperature increases. Increasing the RCA replacement ratio can reduce the initial stiffness of beams. In addition, five design codes including YB 9082, JGJ 138, Europe 4, AISC 360, and AIJ-SRC were employed to evaluate the residual shear capacity of SRRAC beams. Based on the experimental data, a grey correlation analysis was conducted to evaluate the parametric sensitivity of the shear behavior of SRRAC beams. The evaluation results indicate that the selected codes for SRNAC structures are feasible to evaluate the residual shear capacity of SRRAC beams when the exposure temperature is below 600 °C.

Shear capacity of H-shaped steel beam with randomly located pitting corrosion

The H-shaped steel beam is one of the most commonly adopted steel members in building structures and industrial structures, including, bridges, ocean platforms, and industrial equipment. For the steel beams adopted in such structures, corrosion is inevitable, of which pitting corrosion is one of the most common types. The shear capacity of the webs of steel beam is an important performance factor utilized by steel structures. This study aims to reveal the influence of pitting corrosion on the shear capacity of corroded H-shaped steel beams. The relationship between shear capacity and mass loss ratio is the key research content. This study investigates the constant and randomly corroded depths. An analytical method for predicting the residual shear capacity of corroded steel beam is proposed. Results indicate that the proposed method has high accuracy in predicting the shear capacity of H-shaped steel beam with corroded web. The proposed analytical method is applicable for constant and random tw,c/ tw. The conclusions derived in this work are suitable for steel webs with normalized slenderness λs of less than 1 and can be applied to steel beams with different material strengths.

Shear behavior of reinforced recycled aggregate concrete beams after exposure to temperatures up to 600 °C

This study aims to investigate the shear behavior of reinforced recycled aggregate concrete (RRAC) beams after exposure to elevated temperatures. A total of sixteen 1/3-scale RRAC beams with the shear span-to-depth ratio of 1.2 were tested using the four-point bending facility. The method of equivalent total water was employed to manufacture the RAC. Four recycled coarse aggregate (RCA) replacement ratios (i.e., 0, 30%, 70% and 100%) and three elevated temperatures (i.e., 200 °C, 400 °C and 600 °C) were considered to examine their effects on the shear behavior of RRAC beams. The test results indicate that increasing of the elevated temperatures leads to the change of concrete color from smoky-gray to grayish-reddish and results in reducing the shear performance (i.e., load bearing capacity and initial stiffness) of RRAC beams. The shear damage and mechanism of RRAC beams were similar to those of reinforced natural aggregate concrete (RNAC) beams at the same elevated temperatures. A finite element method developed based on ABAQUS was used to simulate the thermal and shear behavior of RRAC beams. The parametric analysis was then conducted to investigate the effect of transverse reinforcement spacing and shear span-to-depth ratio on the shear behavior of the beam. Six design provisions including GB 50010, ACI 318, Europe 2, BS 8110, AS 3600 and JSCE 15 were employed to evaluate the residual shear capacity of RRAC beams. The evaluation results indicate that the existing provisions derived from RNAC underestimate the residual shear capacity of RRAC beams within the temperature equal to 500 °C.

The mechanical behavior of RPC under combined shear and compressive loads

In this study, the shear behavior of reactive powder concrete (RPC) in terms of shear strength and shear slip was studied by direct shear tests on cubic specimens and the influences of water-binder ratio, steel fiber volume ratio and normal compressive stress ratio were investigated. The test results indicated that using a low water-binder ratio and a reasonable fiber content could enhance the shear strength of RPC specimens. The RPC specimen containing steel fiber will not be severed into two individual parts due to the connection of steel fiber. Moreover, the normal stress was the key contribution to the shear strength, and the residual shear capacity was mainly provided by the friction of the shear surface. The cracking of the specimens became more severe but the shear strength in the cyclic horizontal test did not decrease obviously compared with that in the monotonic horizontal test. Applying the twin-shear unified strength theory to the test data, it was indicated that the elliptic curve showed a good agreement. Therefore, the unified twin shear strength theory could predict the proper RPC strength envelope curve under combined compressive-shear stress states.

Residual shear capacity of cold-formed steel-to-sheathing screwed connections at elevated temperatures

Purpose Most previous thermal-mechanical modeling of cold-formed steel (CFS) walls did not consider the failure of screwed connections under fire conditions because of the limited data of such connections at elevated temperatures. Design/methodology/approach In this study, 285 steady-state tests are conducted on CFS screwed connections with single-layer gypsum plasterboard (GPB) and Bolivian magnesium board (BMB) sheathing at ambient and elevated temperatures. The failure of these connections is described as the breaking of the loaded sheathing edge. Findings For the BMB sheathing screwed connections, hydrochloric acid gas is generated and released above 300°C, and the shear strength becomes much less than that of the GPB sheathing screwed connection above 370°C. Hence, BMB may not be suitable for use as the face-layer sheathing of CFS walls but is still recommended to replace GPB as the base-layer sheathing. The major influencing parameters on the shear strength of screwed connections are identified as the type of sheathing material and the loaded sheathing edge distance. Originality/value Based on the previous and present test results, a unified expression for the residual shear strength of screwed connections with GPB and BMB is proposed at ambient and elevated temperatures with acceptable accuracy. It can be used as the basic input parameter of the numerical simulation of the CFS structures under fire conditions.

STRENGTH RECOVERY OF STEEL BRIDGES WITH CORROSION NEAR BEARINGS

A lot of steel plate girder bridges were erected during the rapid growth in the 1960s in Japan. Currently, the condition of those aging bridges has become marked and a problem in society since over 50 years have passed. Particularly, the corrosion-induced deterioration and damage in railway steel plate girder bridges, which have an open deck, is becoming prominent. Despite that, the evaluations of residual strengths and the strengthening methods of corroded bridges are not always enough. Therefore, firstly, this paper shows analytical-based evaluation results that explain how the residual shear capacities of plate girders, having corrosion near bearings, depend on the condition of the corroded surface, such as a vertical stiffener or a web. The results show the fracture mode as buckling changes as well as the residual shear capacity, according to the degree and form of corrosion. Next, this study proposes a reliable reinforcement measure to recovery the shear capacity by applying said evaluation results and analytical models. Finally, the shear capacity could be improved tremendously by simple attachments as reinforced members.

Residual Shear Capacity of Reinforced Concrete Beams after Fire Exposure

The mechanical properties of concrete and steel are seriously degraded under high temperature, so that reinforced concrete (RC) members after fire may not be able to satisfy the prescribed performance. In this study, 27 full-scale RC beams were carried out shear tests to investigate the shear behaviour after fire. A total of 20 beams were subjected to fire on three sides in accordance with ISO 834 standard fire curve, and the remaining 7 beams (which were not subjected to fire) were employed as a reference. The influences of fire time, stirrup ratio, shear span ratio, longitudinal reinforcement ratio, and preloading (40% loading level) were considered. The experimental results indicated that the shear failure mode of the RC specimens after fire exposure was similar to that of the reference specimens. Both the residual shear load bearing capacity and stiffness of the RC beams decreased after being subjected to fire. The loss of shear bearing capacity increased with the heating time. In addition, the ultimate load bearing capacity of specimens with stirrups subjected to the same fire exposure time decreased with an increasing shear span ratio.

Method for evaluating impulsive shear and residual capacity behavior of bolted connections

When structures are subjected to blast, shock, and other impulsive events, the potential for progressive collapse of the structure due to the loss of load bearing members is a significant concern. An understanding of the behavior of bolted connections during and after impulsive events is necessary to predict and prevent collapse of the structure. Relatively little experimental research has been conducted to investigate the behavior of such components subjected to impulsive shear and no experimental studies have evaluated the residual shear capacity of bolts or bolted connections after an impulsive event, which represent the ability to continue carrying gravity design loads. To fill this gap in knowledge, an experimental method was developed to subject bolts and bolted connections to an impulsive shear event and then measure the residual static capacity of the bolt in situ after the event. In the developed methodology, impulsive loads were generated through the use of a high-speed hydraulic actuator to accelerate a flyer mass to a desired impact velocity towards an impulsive shear apparatus, which holds the bolt. A system was designed to be installed within the impulsive setup to apply a quasi-static load after the impulsive event.A small experimental series was conducted using a conservative, low-friction bolted interface to validate the experimental setup and provide initial insights into bolt behavior for modeling purposes. The series of structural bolt experiments under impulsive loads focused on exploring three aspects: 1) the rigidity of the bolts under impulsive loads as compared to static loading conditions; 2) the appropriateness of static and dynamic increase factors under impulsive shear loads for structural bolts; and 3) the characterization of bolt damage in terms of permanent shear deformation as the result of an impulsive loading.

Shear performance of reinforced concrete beams incorporating stiff slender elements

The present work investigates the shear performance of concrete beams reinforced longitudinally with steel rebars incorporating randomly distributed stiff elements known as “needles”. Compared to commonly used fibers, needles function differently in concrete members that carry increasing internal stresses. To measure the effect of needles on the mechanical performance of concrete, 32 longitudinally reinforced concrete (RC) beams and 96 non-reinforced concrete prisms were tested. Among numerous possibilities, the dimensions of the needles used in the present study were selected based on a number of practical considerations. The results showed that the needles increased the peak and residual shear capacity of the reinforced beams significantly. However, the improvements were not greater than those achieved by using the same volumetric content of fibers made of the same material as that the needles were produced from. Based on the measured results and the observation of cracking patterns, guidance for optimizing the geometry of needles and test specimens are provided for future research.