Truss Mechanism Research Articles

STRENGTH EVALUATION OF JOINT S MEMBER WITH REINFORCED CONCRETE MEMBER USING ANCHOR BOLT

The purpose of this study is to clarify stress transferring mechanism and strength evaluation of the joint connected steel member with reinforced concrete member using anchor bolt based on stress transfer from steel member and reinforced concrete member. To clarify stress transferring mechanism of the joint connected steel member with reinforced concrete member using anchor bolt, seven T-shaped assemblages were tested under monotonic loading. From the test results, it was shown that stress transfer from steel member to reinforced concrete member in the joint could be mobilized by transverse reinforcements arranged intensively around anchor bolt. Based on the arch mechanism and the truss mechanism, a method capable of estimating the ultimate strength of the joint was proposed. The predictions were shown to be in good agreement with the test results. In addition, it was shown that this proposed strength model could apply to the ultimate strength evaluation of the exterior beam-column joint using mechanical anchorages on the reinforced concrete structure.

PREDICTIONS ON STRENGTH OF INTERIOR STEEL BEAM - REINFORCED CONCRETE COLUMN JOINT

Based on stress transferring mechanism and resistance mechanism, the bearing and shear strength formulae of through beam type beam - column joint for RCS system were proposed. It was assumed that S beam - RC column joint was composed of inner and outer panel , and the ultimate strength of beam - column joint was obtained by superposition of the ultimate strength of both panels. In the inner panel, bearing failure was caused by prying action and shear failure was the compression failure of concrete struts surrounded by the flanges and face bearing plates. On the other hand, outer panel was considered to be resisted by arch and truss mechanism. These proposed formulae were shown to be in good agreement with the previous test results. Based on these formulae, design formulae to estimate the strength of the joints were proposed.

Shear strengthening of reinforced concrete beams with CFRP

The current paper reviews existing design guidelines for strengthening beams in shear with carbon fibre reinforced polymer (CFRP) sheets and proposes a modification to Concrete Society Technical Report TR55. It goes on to present the results of an experimental programme which evaluated the contribution of CFRP sheets towards the shear strength of continuous reinforced concrete (RC) beams. A total of seven, two-span concrete continuous beams with rectangular cross-sections were tested. The control beam was not strengthened, and the remaining six were strengthened with different arrangements of CFRP sheets. The experimental results show that the shear strength of the beams was significantly increased by the CFRP sheet and that it is beneficial to orientate the FRP at 45° to the axis of the beam. The shear strength of FRP strengthened beams is usually calculated by adding individual components of shear resistance from the concrete, steel stirrups and FRP. The superposition method of design is replaced in Eurocode 2 by the variable angle truss model in which all the shear is assumed to be resisted by the truss mechanism. The current paper proposes a methodology for strengthening beams with FRP that is consistent with Eurocode 2.

SHAPE OPTIMIZATION OF COMPLIANT MECHANISMS FOR SEISMIC ISOLATOR MODEL

A new concept is presented for seismic isolation system using a compliant mechanism. Optimization approach is utilized for generating a truss structure that has specified equilibrium path, which can be achieved utilizing elastic deformation of a structure and geometrical nonlinearity. The truss structure can be used as a base-isolation system by assigning a path with gradually increasing load with respect to the displacement. Weighted sum of the error of the equilibrium path from the target path is minimized through optimization procedure. The compliant truss mechanism obtained from optimization is designed as the isolator model for the building frame. The effectiveness of our model of isolation system is validated by the result of time history analysis using recorded seismic motions.

EFFECTS OF ASPECT RATIO OF JOINT CORES ON ULTIMATE STRENGTH OF PRESTRESSED CONCRETE BEAM-INTERIOR COLUMN JOINT ASSEMBLIES

Reversed cyclic loading tests were conducted on six prestressed concrete beam-interior column joint assemblies that failed inside the joint cores. The variables adopted in the tests were aspect ratio of joint cores and concrete compressive strength. No significant differences in the maximum shear stress of the joint cores were observed between the beam-column joint assemblies. Finite element analysis of the beam-column joint assemblies was performed. The analytical results showed the presence of 45° truss mechanism inside the joint cores. Equations using 45° truss model was proposed for predicting the ultimate strength of prestressed concrete beam-interior column joint assemblies that failed in shear inside the joint cores. The equations were compared with test data on 26 prestressed concrete beam-interior column joint assemblies that failed in the joint cores. The test results agreed well with the estimations.

Bond Action Effect of Longitudinal Cut-Off Bars on Shear Transfer Mechanism of RC Beams

A method is proposed to estimate the required length of double-layered flexural reinforcing bars for reinforced concrete (RC) beams. This research deals with deep beams in which the shear reaction is dominant and the plastic hinge is not formed. The ACI (American Concrete Institute) and AIJ (Architectural Institute of Japan) guidelines propose several methods to determine the cut-off length of double-layered bars for typical foundation beams. However the theoretical and experimental bases are not yet presented. A series of experimental works was conducted to measure the bond strength of double-layered bars. A method to estimate the double-layered length and the shear strength of beams with small shear span-to-depth ratio is then developed based on the concept of the partial truss mechanism.

Shape morphing hinged truss structures

Truss structures are widely used for the support of structural loads in applications whereminimum mass solutions are required. Their nodes are normally constructed to resistrotation to maximize their stiffness under load. A multi-link node concept has recentlybeen proposed that permits independent rotation of tetrahedral trusses linked by such ajoint. High authority shape morphing truss structures can therefore be designed by theinstallation of linear displacement actuators within the truss mechanisms. Examples ofactuated structures with either linear or planar shapes are presented and their ability tobend, twist and undulate is demonstrated. An experimental device has been constructedusing one-way shape memory wire actuators in antagonistic configurations that permitreversible actuated structures. It is shown that the actuated structure displacementresponse is significantly amplified by use of a mechanically magnified design.

Dynamic Analysis and Simulation of Deployable Planar Truss Mechanism

This document researches on the improved deployable planar truss mechanism design and builds an dynamic equation of the model based on Lagrange equation in the multi-body system dynamic theory. The dynamic model is established to simulate the motion of the system and calculate the force condition of members respectively by ADAMS. Finally, the significant references for the elasto-dynamic analysis and optimization design of the truss mechanism will be provided.

Synthesis of Bistable Compliant Structures from Truss Mechanisms

Synthesis of Bistable Compliant Structures from Truss Mechanisms

Application of plasticity theory to reinforced concrete deep beams: a review

This paper reviews the application of the plasticity theory to reinforced concrete deep beams. Both the truss analogy and mechanism approach were employed to predict the capacity of reinforced concrete deep beams. In addition, most current codes of practice, for example Eurocode 2 and ACI 318-05, recommend the strut-and-tie model for designing reinforced concrete deep beams. Compared with methods based on empirical or semi-empirical equations, the strut-and-tie model and mechanism analyses are more rational, adequately accurate and sufficiently simple for estimating the load capacity of reinforced concrete deep beams. There is, however, a problem in selecting the effectiveness factor of concrete as reflected in the wide range of values reported in the literature for deep beams.

Bond-Strengthening Hooks for RC Members with 1300 MPa-Class Shear-Reinforcing Spirals Part III: Bond Strengths of Double-Layered Longitudinal Bars and Cut-Off Bars

This paper presents an experimental investigation of reinforced concrete (RC) beams with double layered longitudinal bars, bond-strengthening hooks and 1300 MPa-class spirals. The hooks made of mild steel increased the bond strength along longitudinal bars. This experiment is aimed at quantification of not only the effectiveness of the spirals and bond-strengthening hooks on the RC members consisting of double layered longitudinal bars but also the influence of cut-off bars in an inner (second) layer. Twelve specimens were prepared and subjected to cyclic shear loads. All the specimens failed because of bond splitting along the longitudinal bars. The hooks, made of mild steel, increased the bond strength along the longitudinal bars.Applying the bond-strengthening hooks was found to improve the shear capacities of the specimens with the cut-off bars. The authors developed a truss mechanism model for members with longitudinal bars in an inner (second) layer. The model showed that the shear strength depends on the span/depth ratio L/D and inner (second) layer bar length Ld.

EXPERIMENTAL STUDY ON SHEAR STRENGTH AFFECTED BY SPLITTING BOND FAILURE OF R/C COLUMNS STRENGTHENED LATERALLY WITH EXTERNAL PC RODS

This paper aims to investigate the shear strength, which is affected by splitting both failure of the longitudinal re-bars, of R/C columns laterally strengthened with external PC rods. The results of cyclic loading tests indicate that the shear strength is much higher than that of predictions by an existing method based on the combination of truss and arch mechanisms. The shear strength can be predicted better if the effect of cover concrete on the bond stress of longitudinal re-bars required in the truss mechanism is taken into account.

ULTIMATE SHEAR STRENGTH OF PRESTRESSED CONCRETE MEMBERS CONSIDERING BOND STRESS OF PRESTRESSING STEEL

Analytical methods based on truss and arch mechanisms were proposed to predict the ultimate shear strength of prestressed concrete members. Yielding of longitudinal mild steel bars and prestressing tendons were taken into account. Bond capacity of prestressing tendons was also included in the analyses. Test results from 119 prestressed concrete beams and columns in the past literature were compared with the analytical results in terms of the ultimate shear capacity. The proposed methods gave a better and more accurate estimation of the ultimate shear capacity than the method provided in the standard for design and construction of prestressed concrete structures published by Architectural Institute of Japan. The accuracy did not depend on the experimental parameters such as shear reinforcement ratio, axial force level, shear span ratio and concrete compressive strength specified for the specimens.

Proposed macro-model for the analysis of infilled frame structures

Reinforced concrete frames infilled with masonry panels constitute an important part of the high-risk structures in different regions of high seismicity. In some developing countries, they are still used as main structural system for low to medium rise buildings. Consequently, reliable methods to analyse infilled frames are required in order to reduce the loss of life and property associated with a possible structural failure.
 The equivalent strut model, proposed in the 1960s, is a simple procedure to represent the effect of the masonry panel. Several improvements of the original model have been proposed, as a result of a better understanding of the behaviour of these structures and the development of computer software. This paper presents a new macro-model for the evaluation of the global response of the structure, which is based on a multi-strut formulation,. The model, implemented as 4-node panel element, accounts separately for the compressive and shear behaviour of masonry using a double truss mechanism and a shear spring in each direction. The principal premises in the development of the model are the rational consideration of the particular characteristics of masonry and the adequate representation of the hysteretic response. Furthermore, the model is able to represent different modes of failure in shear observed for masonry infills. The comparison of analytical results with experimental data showed that the proposed model, with a proper calibration, is able to represent adequately the in-plane response of infilled frames.

Lap Splices Anchored by Headed Bars

This research aimed to experimentally study the anchorage behavior of headed reinforcement in lap splices. Observations of cracking behavior, strain measurements of reinforcement, and strength are reported. The behavior of unconfined laps is compared to confined laps, and the behavior of nonheaded and headed bar laps are also compared. Bar stresses are compared with a proposed model for bearing capacity at the head. Test results suggest that noncontact lap splices should be modeled using a truss mechanism with diagonal compression struts between opposing bars. Under such a model, the capacity of the lap is determined by an anchorage length defined by the intersection points of the diagonal struts. Using this model, the anchorage behavior of headed bars is similar to previously reported results from CCT node tests in which anchorage consisted of bond and head bearing components. Results show that headed reinforcement can markedly reduce required lap length of spliced reinforcement.

RC 보에서의 전단저항기구와 주철근의 부착 작용과의 관계

The uniform truss mechanism is widely accepted as a shear transfer mechanism in reinforced concrete members. However, the uniform truss action cannot be expected when the bond stress distribution is not constant along longitudinal bars. A test method in which only the truss action takes place is developed and conducted to investigate the truss actions under various bond contributions. Based on the experimental results and analysis, the following findings can be obtained: 1) The bond stress distribution depends on the axial compression force, the amount of shear reinforcement and loading conditions. 2) The analysis using the combined truss model consisting of uniform and fan-shape trusses can predict the experimental results

Mechanical behaviour and non-linear analysis of short beams using softened truss and direct strut & tie models

This paper discusses the application of the softened truss and strut and tie models on short beams. The softened truss model originally proposed by Hsu is based on three fundamental principles of mechanics of materials, i.e., stress equilibrium, strain compatibility, and constitutive laws of materials. The model has two important characteristics. The first is the non-linear association of stress and strain. The second is the softening of concrete in compression due to tensile strains in the perpendicular direction. For short beams, one of the most important factors influencing behaviour is the effective transverse compression, which is dependent on the shear-span-to-depth ( a / d ) ratio. In this study, the softened truss model is revised so that the model gives more accurate predictions of the shear strength of short beams. The revised softened truss model (RSOTM) has three differences from the original model. In the RSOTM, it is shown that the effective transverse compression is not only dependent on the a / d ratio but also on the reinforcement ratio in the longitudinal direction as well as the size of the specimen. Second, it is shown that the softening phenomenon in short beams is more severe than that assumed in the original model. The third difference is that the effective transverse compression will be zero when a / d ratio exceeds 1.5. The ROSTM is compared with ACI318-2002, which recommends that short and deep beams should be designed by strut and tie models. ACI318-2002 and the final draft of Eurocode 2 do not provide specific guidance on suitable strut and tie models for different cases. In this study on short beams, a strut and tie model which consists of three mechanisms is recommended: a direct strut mechanism to account for the contribution of concrete and two truss mechanisms to account for the contributions of the horizontal and vertical shear reinforcements to the shear strength. It is imperative that ACI 318-2002 and the final draft of Eurocode 2 should be modified so that they should stress the existence of these three mechanisms in short and deep beams.

U字型プレキャスト部材を用い材端で全数縦重ね継手した梁部材に関する実験的研究

For the purpose of comprehending the performance and the bond characteristics of reinforced concrete beam with all lapped splices in beam depth way at the critical region using U-shaped precast beam with longitudinal and transverse reinforcing steel bars, the authors performed cyclic loading tests for beams subjected to bending moment and shear force. In this case, the splicing reinforcing steel bars passed through beam-column joint are put on top of bottom bars(vertical splicing). As the result, it is clarified that 1) length of yield region was 1/2 of beam depth, 2) stress of main bar at end of lapped splice was evaluated by assuming the truss mechanism under the truss angle 45°, 3) the bond splitting strength of vertical splicing was evaluated by considering vertical binding force required to transmit bond force of splicing bar on the basis of assuming the truss mechanism and using the past evaluation of bond splitting strength.

Predicting the failure modes of monotonically loaded reinforced concrete exterior beam-column joints

This study aims at postulating a simple methodology for predicting the failure modes of monotonically loaded reinforced concrete beam-column joints. All the factors that affect the failure modes of joints are discussed in detail using an experimental database of monotonically loaded exterior beam-column joints. The relative contributions of the strut and truss mechanisms to joint shear strength are determined based on the test results. A simple design equation for the beam longitudinal reinforcement ratio for joints with low, medium and high amount of stirrups is developed. The factors influencing the failure modes of monotonically loaded exterior beam-column joints are investigated in detail. Design charts that predict the failure modes of exterior beam-column connections both with and without stirrups are developed. Experimental data are compared with the design charts. The results show that the simple methodology gives very accurate predictions of the failure modes.

RC 柱部材におけるせん断抵抗機構と主筋付着作用との関係

The uniform truss mechanism is widely accepted as a shear transfer mechanism reinforced concrete members. However, the uniform truss action cannot be expected when the bond stress distribution is not constant along longitudinal bars. A test method, in which only the truss action takes place, is developed and conducted to investigate the truss actions under various bond contributions. Based on the experiments and analysis, following findings have been obtained; 1) The bond stress distribution depends on the axial compression force, the amount of shear reinforcement and loading conditions. 2) The analysis using the composite truss model composed of regular and fan-shape trusses can predict the experimental results.