Compression Strut Research Articles

Analysis of Tensegrity Rotationally Repetitive Space Structures Using the Substructuring Method

In this paper, a substructuring method is presented for calculating the displacement of cable domes. This method obtained matrices as a canonical form in cyclic structures using graph theory. This method helps to avoid the generation of the entire matrices. Then, a solution for the eigenproblem is presented and nonlinear equations are solved by the Newton–Raphson method. In this paper, the cable domes are prestressed rotationally repetitive structures that are cyclically symmetric, having cable part and compression strut part. For clarifying the benefits of the proposed method, both the usual method and the substructuring method are performed for some examples. Results show that the time and memory are considerably (more than 80%) saved in the substructuring approach.

First application of the balanced lowering method to build two bridges in Austria

AbstractThis new bridge construction method consists of building the bridge girders in a vertical position and of rotating the bridge girders into the final horizontal position. In order to rotate the bridge girders, additional structural elements, in this case compression struts, are required. In some topographical situations, it will be more efficient to produce the bridge girders with this innovative method than with the traditional incremental launching method or the balanced cantilever method. The span of the bridge girders is reduced by the compression struts, which enables considerable savings in construction materials. This article explains the design and the first application of the balanced lowering method to build two bridges across the Lafnitz and Lahnbach rivers as part of the Fürstenfeld Motorway in the southeast of Austria. The good cooperation of the project participants allowed for the successful first‐time application of the method for the two bridges described in this article. The unproblematic application of the balanced lowering method for the prestressed concrete bridge with 2.0 m high bridge girders proved that considerable savings in resources and costs were possible compared to the originally planned steel‐concrete‐composite bridges with 4.2 and 4.6 m high bridge girders.

Development of a Macro-Model for concrete masonry infilled frames

Masonry walls, when built to infill a frame structure, have been shown to have a significant effect on the strength, stiffness, and seismic properties of the frame structure. The accurate consideration of this effect is crucial in lateral behavior analysis of the infilled frame structures, especially under the seismic loading condition. This study proposes a new macro-model in an effort to developing a practical and rational approach for evaluating the masonry infill contribution in the design of masonry infilled frames. This model accounts for the compressive and shear behavior of the masonry infill as well as the infill effect on the bounding frame. Compressive behavior was represented through compressive struts located in the diagonal direction connecting loaded corners of the infill. Two sets of three struts were used to replace the top and bottom half of the masonry infill. The shear behavior of the infill was captured through a shear spring connecting the two sets of struts at the center of the infill. The struts and shear spring were configured in a serial manner such that both compressive and shear sliding failure can be predicted. The constitutive laws assigned to the struts and spring were based on consideration of orthotropic properties of masonry and experimental observations. This model was verified against the test results of masonry infilled masonry frames obtained in this study and of masonry infilled RC frames reported in the literature. Both monotonic pushover and quasi-static cyclic analyses were considered in the model verification. The results showed that the proposed model is capable of simulating the in-plane response of infilled frames of both materials and in both loading conditions adequately.

A proposed strut efficiency factor for strut-and-tie design of steel fibre-reinforced concrete

Strut-and-tie model (STM) is a lower-bound plastic theory to achieve force equilibrium. It uses a simplified truss analogy method to define the load transfer mechanism in the disturbed region (D-region) in concrete structures. STM was mostly applied in the design of conventional reinforced concrete (RC), and there were few discussions on the use of STM for newer concrete technology, e.g., steel fibre-reinforced concrete (SFRC). SFRC presents opportunities in reducing web reinforcements in serviceability checks and in improving the ductility of D-regions. In this paper, a strut efficiency factor for STM is proposed for the design of SFRC by collecting a database of SFRC deep beams. It was discovered that the strut efficiency factor best fits with a function of the product of the fibre factor and concrete cylinder compressive strength. Baseline deep beam numerical models were developed and calibrated with the experimental load-displacement graphs collected through literature. A parametric study with variables such as concrete cylinder compressive strengths, fibre volumes and strut angles were investigated. The proposed strut efficiency factor was found to have a peak capacity lower than the ultimate load capacity computed in the calibrated numerical models, which justified the safe use of STM as a lower-bound plastic method in SFRC.

Torsional design method used in Eurasia region: A comparative study

AbstractThis study conducted an extensive review and evaluation of torsional design methods specified in SNiP and other international building codes. Unlike thin‐walled tube approach utilized as a key basis of design expressions in ACI 318, CSA, and Eurocode 2, skew‐bending theory is still adopted as torsional design methods specified in SNiP code used through Eurasia region. This comparative study is timely required since there are radical code changes in leading Eurasia countries, such as Russia, Kazakhstan, and Uzbekistan, toward Eurocode from SNiP code. To this end, a total of 253 reinforced concrete (RC) specimens that failed in pure torsion were collected from the literature to compare the analytical accuracy of the torsional design methods specified in various design codes. It was found that the torsional design methods specified in SNiP and CSA codes can estimate the torsional strengths of RC members with good level of accuracy, while Eurocode 2 provided quite conservative results. In addition, the maximum limitations stipulated in each design code on the compressive strength of concrete and yield strength of reinforcements are of importance for the safe and efficient torsional design due to interrelation between reinforcement ratios considering materials strengths and inclination angle of compressive concrete strut.

Dynamic performance of soft-storey structures with gap elements at beam-column joints

Soft-storey structures are more susceptible to failure for seismic vibrations, which is well-known to the world. But, in multi-storey apartments, it is a practice to provide a parking place at the ground storey, inducing soft-storey effects. In the present study, an effort is made to reduce the soft-storey effect on the structure's dynamic performance by introducing an arrangement of gap elements at beam-column joints. To that context, a numerical assessment is carried out to check the performance of the RC structure. The gap element is modelled as a spring either in a beam or in a column or both.The research has been performed in two parts; the first part of the analysis is focused on optimizing the gap element pattern. Diagonal compressive struts replace the infill walls, and the ground storey is modelled as an open ground storey without infill walls, which is considered a soft-storey. From the first part, an optimal gap element pattern from five different arbitrary patterns is obtained from the results of linear dynamic response spectrum analysis, depending upon the comparison of various seismic parameters. The second part of the analysis involves checking the effect of the gap element's optimized pattern for four levels of structures with vertically varied aspect ratios. Response spectrum analysis is performed, and a study is conducted to compare the seismic parameters for the four levels. The models with gap elements have shown an apparent reduction in storey displacements, inter-storey drift ratios, over-turning moments, and increment in storey stiffness when compared to the conventional models, thus exhibiting constructive outcomes.

Performance evaluation of the energy dissipating hysteretic infill wall frame considering opening under in-plane and out-of-plane loading

An energy dissipating hysteretic infill wall system comprising slotted concrete blocks interlinked with energy dissipating link elements is conceptualized and developed. A comprehensive experimental and numerical study is conducted on the energy dissipating hysteretic infill system to prove its efficacy and efficiency over the conventional brick infill system. The energy dissipating hysteretic infills act as passive energy dissipating system with an improvement over the conventional infills such as the arrest of the diagonal compressive strut formation, a stable post-yield behavior for the infilled frame, and a better failure mechanism. The performance of the energy dissipating hysteretic infilled frames is evaluated under uni-axial in-plane loading, out-of-plane loading, and also simultaneous bi-axial loading, considering the effect of opening. The observed behavior is ascribed to the energy dissipation mechanism, which is a combination of the yielding of the energy dissipating link elements and the friction between the blocks. A numerical modeling of the energy dissipating hysteretic infill is developed in OpenSees by calibrating the YamamotoBiaxialHDR element and singleFPBearing element with the experimental test data of the energy dissipating hysteretic infill wall system.

Seismic tests and nonlinear model of beam-CFDST column joints with blind fasteners

In recent years, substantial research efforts have turned towards concrete filled double skin steel tubular (CFDST) column due to its superior mechanical performance. However, an effective and convenient connection method between a CFDST column and a beam still needs to be investigated in depth. This paper tried to adopt the blind bolting technology in a CFDST column to beam connection. A series of joint specimens were prefabricated and designed with different end plate types, column hollow ratios and beam types to carry out pseudo-dynamic tests. Excellent seismic performance was detected for all test specimens. It was observed that increasing the column hollow ratio could moderately increase the ultimate strength and the specimen with extended end plate had higher ultimate strength stiffness compared with that with flush end plate. To accurately capture the dynamic response for this type of joint, an analytical model was developed considering the shear performance of panel zone and moment-rotation behavior of connection. Shear strength of CFDST column panel zone was modified from that of CFST column panel zone based on the yield line method for including the contribution of confined compression strut. It indicated that two potential yield mechanism might appear depending on the column hollow ration (χ). The analytical model could well predict the test results. The research and analytical results provided an effective connection method to assemble a CFDST column to a beam and supply a feasible analytical model to predict the joint performance.

Load transfer mechanism of exterior beam-column joint with unsymmetrical chamfer

This study aims to understand the load transfer mechanism of exterior beam-column joints (BCJs) with unsymmetrical chamfers for strengthening. It comprises both experimental and numerical studies. Four 2/3-scale specimens were prepared including one without joint shear reinforcements as control, one with joint shear reinforcements and two specimens with chamfers installed. They were subjected to constant axial force and tested to failure under reversed horizontal displacements. Based on the experimental results, performance of BCJs can be improved by installing unsymmetrical chamfers. Secondly, parametric studies were conducted via non-linear finite element analysis. BCJs with different sizes of chamfer or ratios of LC/LBC ranging from 0.50 to 1.33 were modelled to study the effect of chamfer size on joint shear strength. Here, LC is size of chamfer; and LBC is minimum dimension of beam or column.It is found that the joint shear strength is further improved with increasing size of chamfer. Minimum ratio of LC/LBC is recommended as 0.67. Lastly, a load transfer mechanism for exterior joint with chamfer is proposed based on strut and tie concept. It takes into account the benefit of additional compressive strut in chamfer in increasing the joint shear strength.

Simplified Equations for Shear Strength of Composite Concrete-Filled Steel Tubes

Shear strength of filled composite members, namely, circular or rectangular concrete-filled steel tubes (CFST) have been investigated in past research. Results established the relative contributions of the steel tube and concrete infill to the total shear strength and showed that the concrete contribution depends on the development of a compression strut in the concrete infill when shear-span values are low. While experimental results and numerical models are available in the literature, simple equations that empirically encompass this behavior are preferable for design purposes. This paper provides an overview of the technical approach that has been followed to propose such equations for consideration and possible implementation in future editions of design specifications. The shear strength obtained using the proposed equation is compared with the shear test database from the existing literature and found to be safe; it accurately captures the contribution of the steel tube to the total shear strength and conservatively approximates that of the concrete.

Incremental inelastic dynamic damage analysis of MRRCFs infilled with masonry panels

Calculus complexity, time-consuming and high computational effort of the nonlinear dynamic analysis coupled with the complexity of simulating the interaction between masonry infill walls and reinforced concrete frames cause this fact that infill panels are usually considered as the non-structural elements to analyze and design the process of reinforced concrete frames infilled with masonry walls. In this study, to predict the influence of masonry infill panels on the imposed damage of moment-resisting reinforced concrete frames (MRRCFs) under earthquake excitation, incremental inelastic dynamic damage analyses are performed several MRRCFs under twenty seismic ground motions. The MRRCFs are simulated once without considering masonry infill wall effect (as bare frames) and another one considering masonry infill wall effect (as infilled frames). The diagonal compression strut model used to simulate the infill walls is compared with some other proposals in terms of the equivalent strut width, the bed-joint sliding shear strength, the diagonal tension cracking strength, the corner crushing strength, and the diagonal compression strength. Results show that the equivalent strut width, the diagonal tension cracking strength, and the corner crushing strength predicted by FEMA306 are in reasonable compliance with the model used in this study. The capacity and damage curves of bare, and partial, and full infilled frames using incremental dynamic analyses are achieved and compared. The consequences proved that masonry infill walls improve the lateral load-bearing capacity of MRRCFs and decrease the imposed damage of these frames in the seismic excitations. Furthermore, two relations are derived to predict the damage of bare and infilled frames under the earthquake excitations. To assess the accuracy of proposed relations, three new frames are designed. The values of their seismic damage are achieved through inelastic damage analyses and presented relations. Comparing the outcomes confirms the validity of proposed relations.

Modelling of infill walls in reinforced concrete buildings under low-amplitude vibrations

A study was undertaken to analyse the capability of conventional finite-element (FE) models to represent the actual dynamic behaviour of masonry infill walls in reinforced concrete (RC) buildings under ambient conditions. Two commonly used modelling techniques were examined – shell elements and diagonal compression struts. An existing non-symmetrical, six-storey RC building was used as a reference structure. The dynamic characteristics of the real building were determined by an ambient vibration survey. Two FE models of the building were then constructed and the dynamic characteristics of the building were determined numerically. Comparisons of the experimentally obtained dynamic properties and those obtained using each numerical model revealed the most appropriate method for visualising the dynamic behaviour of RC buildings under low levels of vibration. The dynamic behaviour of RC buildings under earthquakes and the use of code-based period estimation formulas were then analysed. The results showed that each modelling technique affected the predicted dynamic frequencies substantially; choosing the most suitable model depends on the level of vibration.

Numerical analysis on tensile capacity of loop connections

Cast-in-place joints are commonly used as an on-site connection for precast assembled bridge concrete elements. The reinforcements in traditional cast-in-place joints usually are tied or welded, which takes more time and increases construction time. With advantages of the construction convenience and the small joint length, loop connections are gradually adopted by recent practice engineering. The strut-and-tie model is currently often used to calculate the tensile capacity of loop connection, but the current model based on geometric structure fails to consider the influence of the adjacent U-bars and the transverse reinforcements. In this paper, numerical models of loop connections are established and verified with the experiments to reveal the effect of the adjacent U-bars and the transverse reinforcements. Parametric analyses are then developed to reveal the force mechanism of loop connections. Finally, a modified strut-and-tie model considering the effective strength and the width of the concrete compressive strut is proposed, and the simplified calculation method of tensile capacity of loop connections is proposed.

Comparative analysis of EC2-04 and ACI318-19 strength provisions for reinforced concrete beams under pure torsion

While the EC2-04 and ACI318-19 provisions use almost the same philosophy to evaluate the torsional strength of reinforced concrete beams, some important details and limitations in these two approaches differ greatly. The objective of the present study is to investigate the differences between these codes and their accuracy by how well they estimate the torsional strength of experimentally tested beams. The predicted torsional strengths based on EC2-04 and ACI318-19 approaches were compared with the results of 120 tested reinforced concrete beams under pure torsion. The inclination angle of the concrete compression struts of the idealized space truss model is chosen to be equals to 45°. It was observed that the ACI318-19 approach is more conservative than the EC2-04 approach in predicting the torsional strength of the tested beams. The graphical comparisons of the predicted to tested torsional strength ratios shows that the EC2-04 approach gives approximately normal distribution curve with a peak at a strength ratio of about 0.85.

Experimental analysis of a modified two-step corbel for precast concrete system

Concrete corbels are the most common component used in connections of precast concrete structures. The industrial production system is especially difficult when multi-planar corbels with different shapes are used. To overcome this problem, the column may be cast without corbels, which are instead cast in a second stage after the column has been stripped from the mould. This system can improve the industrial production and reduce the openings and cut-outs in the formwork. In the two-step corbel system analysed in this paper, fully anchored threaded couplers are placed in the column mould and used in a second stage to splice the main reinforcement of the corbels. Different treatments of the column–corbel interface and two applied load eccentricities are analysed. Thirty-four specimens with a monolithic corbel or a two-step corbel are tested. The corbel strength and crack width of the column–corbel interface are measured by experimental tests. Alternatives are suggested to the two-step corbel system; that is, the use of a loop reinforcement crossing the interface to reduce the interface crack width and the use of 80 kg/m3 steel fibres to replace the secondary reinforcement of the corbel. This solution showed the same strength and interface crack width as monolithic corbels under the service limit state. The addition of steel fibres to the corbel did not have a significant influence on its strength. However, the steel fibres were necessary to guarantee a ductile failure of the compression strut in the absence of secondary reinforcement in the corbel.

Effect of infill wall properties on seismic response of RC structures

Brick infill walls (BIW) have significant effects on reinforced concrete (RC) structures' seismic performances. However, mechanical effects on the structural performance of BIWs, which are regarded as only weight at the design stage, are not considered in many seismic codes. Therefore, seismic performances of new and existing RC structures could not be realistically obtained. This study aims to investigate the effects on the structural behavior of BIWs, stucco types, and soft story. RC structures with and without BIWs are modeled by using the SAP2000 program. BIW is modeled with the equivalent diagonal compression strut method, and mechanical properties of BIWs plastered with conventional and polypropylene fibrous stuccos are taken from literature. Seismic performances of all structures are investigated using the pushover analysis method, according to Turkish Seismic Code-2007 (TSC-2007) principles. Besides, natural periods, rigidities, ductilities and energy dissipation capacities of all structures are obtained. As a result of analyses, it is determined that BIWs have significant effects on structural performances in terms of rigidity and ductility, and fibrous stucco considerably increases RC structures' rigidity and ductility. These walls can even lead to the collapse of structures in severe earthquakes if design engineers don't regard BIWs or BIWs are placed as asymmetric or deficient on the structure.

Shear Capacity and Behaviour of Bending Reinforced Concrete Beams Made of Steel Fibre-Reinforced Waste Sand Concrete.

Inthis paper, we report the results of our research on reinforced concrete beams made of fine aggregate fibre composite, with the addition of steel fibres at 1.2% of the composite volume. The fine aggregate fibre composite is a novel construction material, in which the aggregate used is a post-production waste. Twenty reinforced concrete beams with varying degree of shear reinforcement, in the form of stirrups with and without the addition of steel fibres, tested under loading. The shear capacity results of reinforced concrete beams made of the fine aggregate fibre composite being bent by a transversal force, as well as the cracking forces causing the appearance of the first diagonal crack, are discussed. The stages of functioning of such elements are described. Furthermore, the effect of the steel fibres on the reduction of diagonal cracking is analysed. Computation of the shear capacity of the tested elements is performed, based on the Model Code 2010 and RILEM TC-162 TDF standards, for two variants of the compression strut inclination angle θ that measured during testing, and the minimum(in accordance with the Model Code 2010 standard). We found that the SMCFT method part of Model Code 2010 showed the best compatibility with the experimental results. The tests and analyses performed demonstrate that the developed novel fibrecomposite—the properties of which are close to, or better than, those of the ordinary concrete—can be used successfully for the manufacturing of construction elements in the shear capacity aspect. The developed fine aggregate fibrecomposite could serve, in some applications, as an alternative to ordinary concrete.

Residual shear strength of reinforced concrete slender beams without transverse reinforcement after elevated temperatures

Forty-eight reinforced concrete (RC) beams without transverse reinforcement were tested at ambient and after exposure to high temperatures. Beams were heated to high steady-state temperatures of 350 °C, 550 °C, and 750 °C in a programmable closed electric furnace and loaded to failure after cooling down. In addition to exposure temperature, tension reinforcement percentage (ρ) and shear-span-to-depth ratio (a/d) were kept as the variables. In the beams tested at ambient and after the elevated temperature of 350 °C, beam action was dominant, and diagonal tension failure was the observed mode of failure. When beams were exposed to 550 °C and 750 °C, beam action almost vanished, and the beams failed due to the failure of a compression strut joining the loading point and the support. After exposure to high temperatures, shear strength loss observed in beams with a lower tension reinforcement ratio was found to be more significant. Whereas, change in a/d ratio had an insignificant influence on the shear strength loss of the beams. An increase in temperature resulted in the decrease of the beams stiffness and increased the deflection corresponding to the ultimate load. An empirical model was also developed from the data of the present study for the prediction of shear strength of RC slender beams exposed to high temperatures.

Cyclic loading test of abnormal joints in SRC frame-bentmain building structure

Due to functional requirements, SRC column-RC beam abnormal joints with characteristics of strong beam weak column, variable column section, unequal beam height and staggered height exist in the Steel reinforced concrete (SRC) frame-bent main building structure of thermal power plant (TPP). This paper presents the experimental results of these abnormal joints through cyclic loading tests on five specimens with scaling factor of 1/5. The staggered height and whether adding H-shaped steel in beam or not were changing parameters of specimens. The failure patterns, bearing capacity, energy dissipation and ductile performance were analyzed. In addition, the stress mechanism of the abnormal joint was discussed based on the diagonal strut model. The research results showed that the abnormal exterior joints occurred shear failure and column end hinge flexural failure; reducing beam height through adding H-shaped steel in the beam of abnormal exterior joint could improve the crack resistance and ductility; the abnormal interior joints with different staggered heights occurred column ends flexural failure; the joint with larger staggered height had the higher bearing capacity and stiffness, but lower ductility. The concrete compression strut mechanism is still applicable to the abnormal joints in TPP, but it is affected by the abnormal characteristics.

Research on shear strength of CFSST column and H-section with beam composite joint of unequal depth

Four concrete-filled square steel tube (CFSST) columns and H-sections with beam composite joints of unequal depth were designed based on existing specifications and manufactured at ⅓ scale. A failure test of the specimens was carried out under lateral cyclic loading. Different height ratios between the left and right beam, ζ, (ζ = 0.52, 0.39, 0.26, 0.13) were tested to analyze the failure mode, hysteresis characteristics, ductility, strain, and deformation of the specimens and the damage characteristics of the structure. An equation was established to determine the shear bearing capacity of the CFSST column and H-section. The results show that shear failure in the joint core area is the dominant failure mode of the specimen. The greater the beam ratio, the smaller the yield displacement of the specimen is, and the earlier the joint core area reaches the yield strain. The damage value obtained from Chen's model is in good agreement with that obtained from the test and accurately describes the damage evolution and damage limit of the specimen from “basically intact” to “completely damaged”. The shear resistance of the joint core area is primarily borne by the steel tube web, the main concrete compression strut in the core area, and the restrained compression strut. The theoretical values and the experimental values of the shear bearing capacity of the CFSST column and H-section are in good agreement, demonstrating the accuracy of the proposed theoretical equation.