Diagonal Braces Research Articles

Comparison of Practical Calculation Methods for Overall Frame Structures with Filler Walls

At present, the calculation of filler wall in building structure industry is usually implemented by the method of cycle reduction. However, the empirical coefficient proposed by the cycle reduction in view of standard is not accurate. The factors such as the number of filler walls and the rate of opening holes in the structure have different effects on the stress of the structure. Because the stiffness degradation of filler wall is different at different floors and under different stress conditions, the determination of equivalent diagonal bracing width is more complicated. It has been a controversial issue that how the new damping filler wall in the industry to establish an effective formula for calculating the cross-section width of equivalent diagonal brace to be applied to the elastic calculation of the first stage of the seismic and the elastic-plastic calculation of the second stage of the seismic in the case of large earthquakes.

Single diagonal precast prestressed concrete bracing for strengthening existing concrete frames

A new method for seismic retrofitting concrete structures is proposed using an X-shaped precast prestressed concrete brace. This PPC brace is made of four precast concrete parts and middle section that are assembled and added to the existing frame. This method has the following benefits: there is no need to work with wet concrete in site or anchor and bolt to the existing frame, which may lead to a fast and economic retrofitting method. The X-shaped concrete brace was made in half size and its efficiency is confirmed. That X-shaped precast prestressed concrete brace was simulated and evaluated by computerized analysis using ABAQUS FEA modeling by authors of this paper earlier, and the proposed brace showed proper results in reducing lateral drifts and that method is considered as a proper method for seismic retrofitting. Here we are suggesting a different setup for the brace, which may lead to faster and more economic strengthening of RC structures. The new setup is omitting the middle section and suggests the brace to be used as a single diagonal. A model of this proposed method is simulated in ABAQUS FEA and the results show it is proper in reducing lateral displacements.

Seismic retrofit of precast soft-storey building using diagonal steel-shape memory alloy bracing device: Numerical investigation

A diagonal steel-shape memory alloy bracing device is proposed for seismic retrofitting of vulnerable building frame structure. Superelastic shape memory alloy bar is put in series with steel bars in the bracing. The device makes use of the loading plateau of superelastic shape memory alloy to limit the tensile force of diagonal bracing. A precast soft-storey building frame in Australia was selected for a case study. A numerical model of the frame was developed and validated with the results from full-scale pull-down field tests. Nonlinear time history analysis was then conducted to evaluate the seismic performance of the frame with different retrofitting strategies. The result shows that the diagonal steel-shape memory alloy bracing can reduce the displacement demand on the soft-storey frame. Meanwhile, the level of tensile force of steel-shape memory alloy bracing can be controlled by the force plateau of the shape memory alloy bar, which is recommended to be 20% of the yielding force of the steel bar. The lower tensile force demand could alleviate the force demand at the associated support connections.

Optimum design of purlin systems used in steel roofs

In this study, one existing purlin system which is used in steel roof is optimized by taking into account less cost and bearing maximum load via developed software. This software runs with firefly algorithm which is one of the recent stochastic search techniques. One of the metaheuristic techniques, so-called firefly algorithm imitates behaviors of natural phenomena. Behaviors and communications of firefly are inspired by this algorithm. In optimization algorithm, steel sections, distance between purlins, tensional diagonal braces are determined as design variables. Design loads are taken into account by considering TS498-1997 (Turkish Code) in point of place where structure will be built, outside factors and used materials. Profile list in TS910 is used in selection stage of cross sections of profile. Constraints of optimization are identified in accordance with bending stress, deformation and shear stress in TS648. Design variables of optimization are selected as discrete variables so as to obtain applicable results. Developed software is tested on existing real sample so; it is evaluated with regard to design and performance of algorithm.

Metal Foam-Filled Tubes as Plastic Dissipaters in Earthquake-Resistant Steel Buildings

The aim of this paper is to investigate whether metal-foam-made devices can be effective to dissipate seismic energy in buildings during strong earthquakes. To this purpose, non-linear numerical analyses of concentrically braced steel buildings under recorded ground motions have been carried out, while some experimental tests on metal-foam specimens and metal-foam-filled tubes have been performed. Foam-based devices are assumed to be inserted within the diagonal braces of the considered steel frame to dissipate energy by plastic deformation during strong earthquakes. To apply the experimental data, a scaled numerical model of the prototype building has been implemented by means of the similitude theory and the Buckingham Π theorem. The results of the study provide a preliminary assessment of the potential of metal foam-based dissipaters to reduce the seismic effects in civil structures.

Bending tests for the structural safety assessment of space truss members

This article compares two nondestructive static methods used for the axial load assessment in prismatic beam-columns of space trusses. Examples include the struts and ties or the tension chords and diagonal braces of steel pipe racks or roof trusses. The first method requires knowledge of the beam-column’s flexural rigidity under investigation, whereas the second requires knowledge of the corresponding Euler buckling load. In both procedures, short-term flexural displacements must be measured at the given cross sections along the beam-column under examination and subjected to an additional transverse load. The proposed methods were verified by numerical and laboratory tests on beams of a small-scale space truss prototype made from aluminum alloy and rigid connections. In general, if the higher second-order effects are induced during testing and the corresponding total displacements are accurately measured, it would be easy to obtain tensile and compressive force estimations.

Improving Seismic Behavior of MRFs by U-shaped Hysteretic Damper Along Diagonal Brace

This paper presents seismic assessment of a U-shaped hysteretic damper as an enhancement system, in moment resisting frames. The proposed system is consisted of a damping box at the middle of a diagonal brace. The box includes U-shaped steel plates welded to the side plates. When a transverse load, like earthquake, is exerted to the building, relative displacement between the stories forms and will be transmitted to the braces where energy dissipation will be achieved by adding a displacement-dependent U-shaped damper. For this purpose, the system is applied to a 2D 2-span 3-story frame to which by applying eight different earthquake records, far-field, near-field and mid-field, seismic response are evaluated. The responses are the roof displacement, inter-story drifts, root mean squared of roof displacement and base shear. Result verification is carried out via calibrating characteristics of this damper with an experimental work on a somewhat similar device conducted at the University of Toronto. The results showed that by using this system, the roof maximum displacement decreased 38.9, 40.0 and 37.1% and the maximum base shear decreased 36.5, 28.5 and 39.5% respectively under near-field, mid-field and far-field records, averagely. Similar results were observed in inter-story drifts and roof displacement RMS.

On the behaviour of mid-connection in off-centre bracing system

This paper presents theoretical and experimental investigations on the behaviour of mid-connections in an off-centre bracing system. This braced system is preferred by architects because of the eccentricity introduced by the diagonal brace members, which allows a wider area of opening in the frame panel. Assumptions when designing the system in two dimensions has led to severe damage of structures based on observations of the recent Bam earthquake. In this regard, the assumption of mid-connection of the brace elements has a significant effect on the behaviour, stability and lateral buckling load resistance of the system. In order to investigate the effect of mid-connection types on the behaviour of the system, two possible implementations of this connection were considered. Based on the slope–deflection method and equilibrium equation at the connection point, the stiffness matrix was obtained to calculate the lateral buckling load of the system. In addition, to validate the theoretical calculation and practical consideration of the system, two frames of one-third scale were fabricated and tested. A good agreement between the experimental results and the theoretical calculations was obtained.

Experimental and numerical study on lateral stability of temporary structures

This paper investigates the lateral performance of temporary structures, which consist of slender members and corresponding joints, under both vertical and horizontal loads. The ultimate bearing capacity, failure modes and the strain distribution of members are illustrated. Experimental results indicate that the lateral stability of the temporary structures is weaker than the vertical stability. Diagonal bracings are the main load-bearing members which resist horizontal loads while the horizontal bars are used to keep stress low. Based on the joint mechanical parameters and the probabilistic models of initial geometric imperfection, the stochastic finite element models (SFEMs) using the Monte Carlo method have been established. The models can consider the semi-rigid performances of joints and initial geometric imperfection. The numerical results demonstrate consistency with structural tests data. Moreover, the influences of structural layers and spans are analysed based on the SFEM. Multiple factors, including spans, layers and upper vertical loads, should be considered when the lateral capacity of temporary structures is calculated. A rapid prediction formula of the lateral stability of temporary structure has been obtained.

Effect of FRP Strengthening on the SHS brace collapse mechanism

During an earthquake diagonal braces are designed to dissipate energy by yielding in tension and buckling in compression. However, local buckling occurring in the middle of the brace leads to immediate fracture. With the aim of strengthening braces against local buckling, wrapping FRP sheets in transverse direction is proposed in this study. Hitherto, the effect of FRP strengthening on the post-buckling behaviour of Square Hollow Section (SHS) tubes has not been investigated. A numerical model was generated and verified by previous research. Then, a comprehensive parametric study was conducted and the effect of slenderness ratio, number of FRP layers and FRP coverage percentage on post-buckling response of strengthening brace was explored within the study. Results indicate that utilising FRP is certainly successful at mitigating local buckling mode of long SHS braces Moreover, for short braces, applying enough numbers of FRP layers can change the mode of buckling from local to overall. Finally, an optimized length of FRP was suggested for strengthening of braces in accordance with their slenderness ratio.

Comparative Analysis of Torsion Resistance Performance between Traditional Support Structure System and Structure with Diagonal Brace

Traditional support structure system of air-cooled condense adopts hybrid structure system of steel truss and reinforced concrete pipe column, and this type of structure has a remarkable torsion effect because that the quality and rigidity is badly non-uniform at the vertical direction. In order to study the natural vibration period, vibration type and dynamic response under multidimensional ground motions, this paper chooses the support structure system with diagonal brace to analysis the dynamic characteristic and lateral-torsional coupled seismic response of the structure, and compares the results with the traditional structures to study the reasons of these changes so as to make recommendations on the designing of structure. The results show that this new-type structure could reduce the torsional effect, lateral displacement and strengthen overall seismic capacity.

Performance based discrete topology optimization of steel braced frames by a new metaheuristic

Seismic topology optimization of structures is a challenging field of structural engineering. So far, a little number of studies has been conducted on this regard and all of them have presented conceptual designs which are of limited practical applicability. The main aim of the present study is to find the practical optimal placement of X- and diagonal bracing systems in steel braced frames subject to seismic loading. To achieve this purpose, a discrete topology optimization formulation is proposed in the framework of seismic performance-based design. A new metaheuristic algorithm, center of mass optimization (CMO), is proposed to deal with the performance-based discrete topology optimization (PBDTO) problem based on the physical concept of center of mass for mass distribution in space. Two challenging benchmark structural optimization problems are presented in order to demonstrate the computational merit of the proposed CMO algorithm compared to a number of algorithms in literature. Furthermore, PBDTO process is implemented for four multi-story steel braced frames by CMO. Performance of the proposed CMO-based discrete topology optimization framework in finding practical topology of bracing members for SBFs is demonstrated on PBDTO examples.

Cold-formed steel framing walls with infilled lightweight FGD gypsum Part I: Cyclic loading tests

In order to improve lateral stiffness and shear strength of cold-formed steel (CFS) framing wall, an innovative CFS wall with infilled lightweight flue gas desulfurization (FGD) gypsum is presented in this paper. For this purpose, six full-scale specimens were tested under cyclic lateral loads. The density and compressive strength of the infilled gypsum were varied to investigate their impacts on lateral stiffness and shear strength of the walls. The failure modes, load-displacement responses, deformability, and energy absorption capacity of the specimens were also investigated. Test observations showed that the infilled gypsum behaved as a diagonal bracing along with wall frames to resist shearing forces. In addition, the failure modes of the infilled walls were characterized by bond-slip cracks between infilled gypsum and wall frames, as well as compressive failure at the corners of gypsum pieces. The peak loads of the infilled specimens were improved by 1.72–2.54 times compared with the unfilled. Besides, the improvement in shear capacity and lateral stiffness of the infilled walls were obtained by increasing compressive strength of the infilled gypsum. When filling identical gypsum into the walls, one with the bigger stub spacing and the stronger sheathing material had the greater lateral stiffness and shear capacity. In addition, a method for determining the resistance factor γR of the infilled specimens was proposed in the paper, which can be used for seismic design.

Finite element modelling of an innovative passive energy dissipation device for seismic hazard mitigation

Nonlinear finite element analyses of an innovative passive energy dissipation device, referred to herein as CAR1, were conducted to investigate its behavior to dissipate seismic energy. The investigated device belongs to the passive energy dissipation systems, as it doesn’t require external power to generate system control forces. It can be used on new or existing structures and can easily be adapted to the particular demands of structures. It can be installed in a variety of ways, including use in either single or cruciate (X) diagonal braces in building frames. Moreover this device has the advantages to provide (i) additional stiffness (ii) dissipation of seismic energy, (iii) as well as control of the axial forces that are developed at the diagonal steel braces. The main part of the device CAR1 is the groups of superimposed blades, which dissipate seismic energy through simultaneous friction and yield. The number and the dimensions of the blades as well as their elastoplastic properties define the constitutive law of the diagonal bars under axial force. To this purpose a finite-element micromodel of the device is formulated and used, by considering contact interface conditions between the blades. The analytical investigation is carried out through an extended comparative parametric study and is focused on the quantitative influence of certain simplified modelling assumptions and several critical modelling parameters on the response of the system. The present paper delineates a set of systematic procedures for finite element model calibration and parametric evaluation that enable robust simulation of the device CAR1 under quasi-static cyclic loading using explicit time-stepping dynamic analysis procedure.

Stability of a pretensioned latticed three-dimensional arch structure with cross cable-strut arrangement

An innovative pretensioned latticed three-dimensional (3D) arch structure with cross cable-strut arrangement is proposed based on the concept of beam string structure with consideration of the indoor headroom. Three cable-strut arrangement schemes of the cable latticed 3D arch are analyzed and the in-plane stabilities of the arches with different cable-strut schemes are compared. Also, the influence of cable anchorage position on the in-plane stability of the pretensioned latticed 3D arch is investigated. The configuration and stability of the parallel cable-arch integral structure with the optimal cable-strut arrangement are studied. The effect of both the transverse diagonal cross bracings and the amount of the longitudinal latticed 3D beams on the buckling mode and stability capacity of the integral structure is studied. Additionally, the relationship between the structural stability capacity and the amount of parallel cable arches is discussed. Two simplified models for stability analysis of the integral structure are presented, and the corresponding calculation accuracies are also discussed. All this work will provide theoretical guidance to the actual engineering application of this structure.

Evaluation of the Effect of End-Connection Specifications on Lateral Bearing Capacity of Concentrically Braced Steel Frames

Concentrically braced steel frames should be capable of bearing considerable amounts of lateral force. The connection of these frames to beams and columns plays an important role in this respect. This connection is designed to either prevent end-connection problems caused by free buckling of a member or reinforce the gusset plate to reduce damages caused by possible buckling of a member at the connection. In order to assess seismic and buckling behaviors of braces under different conditions, 8 single-span one-story frames with diagonal braces were studied using a finite-element software. The first two models were implemented to assess the impact of end clearance, while the other six models were used to study the effects of different stiffeners on the gusset plates. Results showed that, proper incorporation of stiffeners can prevent early failure of the gusset plate connection and enhance post-buckling behavior.

Remarks on Seismic Design Rules of EC8 for Inverted-V CBFs

Chevron concentrically braced frames (C-CBFs) are expected to provide limited ductility in the framework of Eurocode 8: differently from North American codes, lower values of behavior factors are recommended by EN 1998 for C-CBFs than for other concentric bracing configurations (namely diagonal and cross bracings). The research presented in this paper is aimed at revising the design rules and requirements provided for by EN 1998-1 for C-CBFs in order to improve the ductility and the dissipative capacity of this structural system. The proposed design criteria are validated by means of nonlinear dynamic analyses performed on a study case. The results confirm the effectiveness of developed design procedure.

Experimental Investigation on Seismic Behavior of Steel Truss-RC Column Hybrid Structure with Steel Diagonal Braces

This paper aims to provide an experimental support on seismic performance evaluation of the steel braced truss-RC (reinforced concrete) column hybrid structure, which could be applied as the air-cooled supporting structural system in large-capacity thermal power plants located in strong earthquake prone regions. A series of pseudo-dynamic tests (PDTs) and quasi-static tests (QSTs) were performed on a 1/8-scaled sub-structure. The dynamic characteristics, lateral deformation patterns, deterioration behavior, hysteretic behavior and failure mechanisms were investigated. Test results showed that the first vibration mode is torsion, which is caused by the small torsional stiffness of this kind of hybrid structure. The lateral deformation shape is shear mode, and the drift ratio of the structure above the corbel is significantly less than that of the column below the corbel. Earthquake energy is mainly dissipated by the RC pipe columns where cracks mainly occurred at the bottom of column and lower part of corbel. The failure mechanisms were identified indicating that the steel braces improved the global stiffness and modified the load transfer mechanism. This study affirms that the steel braced truss-RC column hybrid structure has the sufficient ductility and good energy dissipation capacity to satisfy the design requirements in high seismic regions.

Evaluation of seismic criteria of built-up special concentrically braced frames

In this paper, seismic provisions related to built-up special concentrically braced frames (BSCBFs) are investigated under cyclic loading using non-linear finite element analysis of a single-bay single-story frame. These braces, which contain double angle and double channel brace sections, are considered in two types of single diagonal and X-braced frames. The results of this study show that current seismic provisions such as observing the 0.4 ratio for slenderness ratio of individual elements between stitch connectors are conservative in BSCBFs, and can be increased according to the type of braces. Furthermore, such increments will lead to decreasing or remaining the current middle protected zone requirements of each BSCBFs. Failure results of BSCBFs, which are related to the plastic equivalent strain growth of members and ductility capacity of the models, show that the behaviors of double channel back-to-back diagonal braces are more desirable than those of similar face-to-face ones. Also, for double angle diagonal braces, results show that the failure of back-to-back BSCBFs occurs faster in comparison with face-toface similar braces. In X-braced frames, cyclic and failure behaviors of built-up face-to-face models are more desirable than similar back-to-back braces in general.

Comparative study of strengthening strategies for reinforced concrete frame with soft ground story

One of the common forms of reinforced concrete (RC) framed building is to provide parking facility at ground level which is created by not providing any infill masonry at parking floor level. Due to the presence of infill walls in the entire upper story except for the ground story makes the upper stories much stiffer than the open ground story resulting in their poor performance during earthquakes. So strengthening of such reinforced concrete (RC) frame buildings with an open ground story is indispensable. In the present study several Strengthening options were evaluated for their effectiveness in improving the performance of such building without disturbing the parking facility of ground story based on linear and nonlinear analysis. The strengthening techniques studied were changing column dimension, providing diagonal bracing, lateral buttresses, shear wall, and providing chevron. The Strengthened building results were compared with the results of the original structure to deduce the structural performance improvement and cost associated to each solution were determined to develop cost efficiency relation for different strengthening technique. Providing lateral buttresses in the open first story was found to be more feasible in both case of increase ground story strength and economic point of view among all strengthening options.