Horizontal Bracing Research Articles

Adding composite truss to improve mechanical properties of reinforced concrete T-girder bridge

To solve the problem of insufficient transverse connection of T-girder bridges, this paper investigated the strengthening method of two composite trusses symmetrically installed in mid-span. The composite truss included two top plates, four diagonal braces, and one horizontal brace. An experimental investigation was carried out to study the mechanical properties of reinforced concrete T-girder using single-point loading method under four load cases. The experimental results showed that the maximum transverse stiffness of T-girder specimens strengthened with composite trusses improved by 12.4% compared with control beams. Simultaneously, it had an excellent restraining effect on the cracks development. The maximum percentage decrease in the deflection corresponding to the maximum load when the reinforced concrete T-girder strengthened with composite trusses over the control beam of up to 39.7 was observed. In addition, the load transverse distribution coefficient was investigated according to rigid-jointed slab (girder) method. The composite trusses were chosen as intermediate diaphragm to calculate moment of inertia. The analytical model was in an accurate with the experimental result under the same loading condition. The optimize spacing of composite trusses was given from 600 mm ( L/10) to 1200 mm ( L/5), and thickness of top plate was 30 mm when the load transverse distribution coefficient was homogeneously distributed. Finally, a three-dimensional finite element model was used to evaluate the effectiveness of composite trusses.

Numerical evaluation on collapse-resistant performance of steel-braced concentric frames

Steel-braced concentric frames (SBCFs) are a popular form of structure and has been widely employed in seismic regions owing to their high strength and elastic stiffness; however, the effects of key parameters on the collapse behavior of SBCFs are unclear due to insufficient investigations, which should be further explored in column removal scenarios. To this end, numerical models were employed to explore the key parameters affecting the collapse behavior of SBCFs in this study. The numerical models of steel frames with or without braces were validated based on previous experimental results. According to the refined model, the effects of brace members of various types and with different slenderness ratios on the collapse behavior were illustrated. The results showed that an X brace type with smaller slenderness ratio is the most appropriate for enhancing robustness against progressive collapse. Thereafter, full-scale numerical models were established to investigate the effect of the column removal position, and the results showed that the frame relied purely on flexural action in a side column loss. Moreover, the effect of the position of horizontal brace layers on the collapse behavior was investigated in the middle and side column removal scenarios. To gain deeper insight into the load-resisting mechanisms, the specific contributions to the total resistance of different mechanisms in different stories, bare steel frames and braces, and tensile and compressive braces were separated. Finally, a strategy for the robustness enhancement of high-rise steel frames was empirically proposed, and it was suggested that the provision of a brace layer for approximately every 10 stories would be effective for the anti-collapse design of high-rise buildings.

Old Iron and Steel Bridges. Historical and technical notes Static and strength of lattice truss girders. Part 4 (Conclusion)

A model was composed only of linear finite elements to simulate 5 consecutive spans (64m+3x66m+64m) of the D. Luiz bridge deck. It integrates the two main girders of the deck, the two horizontal bracings that exist between their upper and lower chords and the transverse vertical bracings located on the same planes of the girders’ verticals. It is already known (see previous parts of this article) that the diagonals of the trusses are single angles, the verticals are double angles and the chords are T-sections, formed by plates and angles, as it happens in many of the lattice truss girders built at that time (second half of the XIX century, first decades of the XX century).

Lateral load bearing characteristics of light gauge steel and lightweight concrete shear walls

In China, there is a new structural system named light gauge steel and lightweight concrete (LSLC) structure, which used lightweight concrete as structural material in composite way with cold-formed steel. Here, the shear walls are the main structural members for the LSLC structure, which are assembled with the light gauge steel lattice columns and horizontal braces, and filled with lightweight concrete. In this study, the LSLC shear walls are experimentally investigated to evaluate their failure mechanism and lateral load bearing capacity. For this purpose, several specimens with different shear span ratio are designed and tested under static cyclic loading. This paper presents the damage state and hysteresis loops of the specimens detailly. Then, the lateral load bearing characteristics of the LSLC shear walls are discussed according to the failure mechanism, such as shear and flexural failure. Finally, the calculation methods of lateral strength for the LSLC shear walls are proposed based on the diagonal strut mechanism and sectional force equilibrium.

Seismic Performance of RC Split-Foundation Frame Structures with Steel Braces in the Mountainous Area

Reinforced concrete (RC) split-foundation frame structures are widely used in mountainous areas. There are two grounding terminals with different heights in the split-foundation frame structures. Under the earthquake, the local damage phenomenon of the structures is severe due to the uneven stiffness distribution. It is one way to improve the seismic performance of the split-foundation frame structures to install steel braces in the upper embedding floor. According to the deformation characteristics of the upper embedding floor, three types of steel braces arrangement for the split-foundation frame structures were proposed: horizontal braces, V-type braces, and V-[Formula: see text] braces. Then based on the ratio of lateral stiffness of steel braces and concrete frame columns, the section of steel brace was designed. A quasi-static test was carried out to analyze the influence of steel braces on the failure mode of the RC split-foundation frame. The reasonable seismic waves were selected to carry out the nonlinear dynamic time history analysis. Then the seismic response and failure mode of the split-foundation frame structures with different braces arrangements were compared. On this basis, fragility analysis was carried out, and the earthquake-induced collapse resistance capacity of split-foundation frame structures with steel braces was preliminarily evaluated. The results show that the horizontal steel brace can improve the phenomenon of damage concentration of the split-foundation frame structures. Furthermore, setting V-shaped braces can significantly reduce the damage degree of the upper embedding end columns and change the phenomenon of locally severe damage of the split-foundation frame structures. Moreover, according to the design method proposed in this paper, setting steel braces can improve the seismic collapse resistance capacity of the split-foundation frame structures.

Design Forces of Horizontal Braces Unlocated at Middle of Columns considering Random Initial Geometric Imperfections

The horizontal bracing forces of column-bracing systems derived from past studies and current design codes were considered only located at middle of columns. Actually, the horizontal braces used to reduce the out-of-plane effective column lengths are frequently designed not to locate at middle of columns. In this paper, a large number of column-bracing systems with the horizontal braces unlocated at middle of columns were modelled and analyzed using the finite element method, in which the random initial geometric imperfections of both the columns and the horizontal braces unlocated at middle of columns were well considered by the Monte Carlo method. Based on the numerical calculations, parametric analysis, and probability statistics, the probability density function of the horizontal bracing forces was found, so that the corresponding design forces of horizontal braces unlocated at middle of columns were proposed which were compared with the design mid-height horizontal bracing forces in the previous study and the relevant codes. The results indicate that the design forces of the horizontal braces located at 0.6 column height are smaller than the mid-height horizontal bracing forces in the previous study while the design forces of horizontal braces located at 0.7 column height are larger than the mid-height horizontal bracing forces in the previous study. The proposed design forces of the horizontal braces located and unlocated at middle of columns are both smaller than the mid-height horizontal bracing forces stipulated in GB50017-2017, Eurocode 3-1992, and AS4100-1998. The above conclusions provide references for the engineering applications and further related code revisions.

Stresses & Strains in Plate Girder with Different Bracing Systems under Combination of Loadings

Abstract: Lateral buckling is one of the most important factors in the design of steel plate girder. This buckling in the girder can be controlled by many methods. The most popular method is to add the intermediate bracing systems along the length of girder. The unsafely designed intermediate bracing systems can easily lead to serious consequences in the construction stage due to lateral buckling by torsion which happens rapidly and suddenly when the internal force in girder exceeds the ultimate value. Reversely, if the intermediate bracing systems are designed excessively, their specific stiffness will be larger than the required one then it is very costly in both material and installing process In the present study different types of torsional bracing systems are used in twin plate girder of span 8m. As the behavior of plate girders with different type of bracing system changes differently along the length and depth. Changing the layout of bracing systems could also make the design easy and more economical. Keywords: Cross-frame Bracings, Horizontal Bracings, Plate Girder, Finite Element Analysis

Mechanical behaviour of a novel floor system with horizontal K-shaped brace in Long-span High-speed railway steel truss Cable-stayed bridge

In this study, a novel floor system with horizontal K-shaped braces was applied to long-span high-speed railway steel truss cable-stayed bridges to reduce the crossbeams’ out-plane bending moment which is significant in the traditional stringer-crossbeam floor system. Based on the new floor system of Beijiang Bridge, a 1:4 scaled floor system specimen was experimentally tested; subsequently, two detailed finite element (FE) models for comparison of the specimen were established to investigate the stress distributions, force transferring and deformation characteristics. Furthermore, the ratio formula of the longitudinal force transmitted by the K-braces to that by crossbeam was determined. The results of the comparative analysis of FE models indicate that the horizontal K-shaped brace can reduce 81.0% of the crossbeam’s maximum stress caused by the out-plane bending moment and alleviate the longitudinal deformations. The measured stresses of the model increased linearly with the applied load from 0.4 to 2.2 times the maximum tension force cases. The K-shaped brace mainly bears axial force; additionally, the out plane bending moment of the crossbeam is small. The longitudinal force transmission ratio is determined by the geometric parameters of the floor system structure, such as section area Ak of the K-shaped brace, and the distance between the side stringer and the lower chord Lc (rather than load type or value). The longitudinal force transmission ratio calculated by experimental and numerical stresses were in the ranges of 1.35 to 6.46 and 1.39 to 7.30, respectively. This indicates that the horizontal K-shaped brace transmits 57.45 to 86.60 % and 58.16 to 87.95 % of the longitudinal force, for experimental and normal stresses, respectively. The similar ratio ranges in both cases reveal that the K-shaped brace can effectively transfer longitudinal forces, reduce the out-plane moment of the crossbeam, and improve the mechanical characteristic of the floor system.

Numerical Simulation of Soil Displacement and Settlement in Deep Foundation Pit Excavations Near Water

Advancing urbanization in China requires large-scale high-rise construction and underground transportation projects. Consequently, there is an increasing number of deep foundation pits adjacent to water bodies, and accidents occur frequently. This study uses a numerical simulation method to study the stability of the deep foundation pit near water based on the Biot three-dimensional seepage-stress coupling model, with the open-cut section on the south bank of the Jinan Yellow River Tunnel Project as the engineering field test. This indicates the following: (1) the maximum horizontal displacement of the diaphragm wall occurred in the fifth excavation stage, and a horizontal brace effectively controlled the inward horizontal displacement of the foundation pit; (2) considering the effect of seepage in the soft soil foundation, the maximum vertical displacement of the ground surface at each excavation stage occurred adjacent to the underground continuous wall. As the depth of the foundation pit increased, the vertical surface settlement decreases gradually in the direction away from the excavation face; (3) considering the seepage conditions, within each interval of excavation of the foundation pit, the horizontal displacement of the continuous underground wall and ground settlement declined; and (4) the numerical simulation and field monitoring data were in good agreement. Under the conditions of accurate model simplification and parameter selection, numerical simulations can adequately forecast conditions of the actual project.

Member capacity-based progressive collapse analysis oftransmission towers under wind load

The wind-induced collapse of transmission towers has raised many concerns. Progressive collapse analysis is recognized as a promising method for the assessment of the collapse-resistant capacity of the transmission tower. The finite element model of an actual transmission tower is firstly built for the analysis, in which the dynamic behavior of the member in failure is taken into account to be in accord with the actual tower collapse. The analysis considering the main design load cases is conducted in advance to determine the case under which the tower has the potential to collapse. The incremental dynamic analysis in association with the explicit time integration algorithm is employed to perform a progressive collapse analysis, where the wind loads are simulated by using the linear filtering method, and the developed failure criterion with axial force and bending moment involved is based on the stability bearing capacity of the members. It is found the tower collapse begins with the horizontal bracing member near the waist. Then, the adjacent members, including the leg members, fail sequentially, and the tower collapses eventually with a shear-type failure. The demand to capacity ratio (DCR) in terms of bearing capacity of the member is defined to quantify the structural behavior, the location of the member that has the potential to fail, and when the initial failure occurs are thereby identified. It is concluded that compared to the member capacity-based analysis, the ultimate strain-based analysis, which is most likely to be an inelastic dynamic analysis permitting a large deformation, may overestimate the bearing capacity of the structure in wind-induced collapse.

Elastic-Plastic Analytical Solution for SEMI’s Horizontal Brace with a Circumferential Through Crack under Tension and Bending

The elastic-plastic behavior of semi-submersible’s horizontal brace with a circumferential through crack which lies at its boundary was studied. Both tension and bending were considered to investigate the closed-form analytical solution. The results indicate that the tensile plastic zone and crack tip opening displacement (CTOD) on the cracked section increase sharply after a smoothly increment when loads became larger. The cracked horizontal brace with a greater initial circumferential through crack has a larger tensile plastic zone and earlier compressive plastic zone appearance on the cracked section. Compared with the load of tension, the bending load has larger effect on the plastic zones of the cracked section and CTOD of the crack. Introduction Since the first semi-submersible platform (SEMI) named as “Ocean Driller” which was designed for drilling wells in the ocean, the SEMIs have gained popularity in the recent decades with ongoing development in oil and natural gas exploration in deepwater. Because of the high risk of environment pollution and casualties of operators which a destruction accident of SEMI might bring, making sure the structure is safe during its service life has become the most important task of SEMI designers and operators. Although the safety design standards for SEMI structures are quite strict, cracks inescapably are initiated during their service life. According to the destruction accidents happened before, Moan (2009) and Zaron et al. (2015) found that the cracks often occur at the horizontal braces which function as the supporting structures in SEMIs and bear complex loads. The presence of such cracks at critical locations can compromise the safety of the braces and then can cause serious disaster eventually. Because of the initial fracture of a horizontal brace, e.g., the accident of Alexander Kielland platform, the loads were transferred to the other braces and led them break because of the overload (see Colin et al. [2014]).

Analysis of the influence of erection of scissor braces on the bearing capacity of the wheel-buckled steel pipe supporting formwork system

The supporting formwork system as one of the most commonly used temporary structures in the process of building construction, its safety accidents frequently occur. The wheel-buckled steel pipe supporting formwork system is a new type of system developed under this background, and scissor brace as a kind of component in the system, have played an important role in improving the bearing capacity of the system. This paper uses ABAQUS finite element analysis software to establish an accurate simulation model of the foundational frame, and on the basis of this model, explores the influence of different erection methods of vertical and horizontal scissor braces on the overall bearing capacity of the frame. When erecting vertical scissor braces to reinforce the foundational frame, priority should be given to erect on the outer facades around the frame, and secondly consider satisfying the arrangement on the three facades. In the process of erecting horizontal scissor brace, the priority of the erected horizontal layer should be considered, that is the sub-bottom horizontal layer, sweeping rod horizontal layer, middle horizontal layer, sub-top horizontal layer, top horizontal layer.

Numerical Modeling for Nonlinear Static Pushover and Response History Analyses of Dhajji-Dewari Structures

ABSTRACT This paper presents a simplified numerical modeling technique for nonlinear static and dynamic seismic analysis of Dhajji-Dewari structures. The technique comprised idealizing timber beam/column members as an elastic beam-element, diagonal and horizontal braces as an inelastic beam-element with fiber-section, and the connection capacity is simulated using lumped plasticity hinges for tension/rotational resistance. A numerical model prepared for a wall tested under quasi-static cyclic loading was analyzed using a nonlinear static pushover analysis procedure demonstrating an excellent performance of the numerical model in predicting the lateral resistance-displacement response. The technique was extended to a three-dimensional building investigated under shake-table tests, showing promising behavior of the numerical model in predicting the displacement response history of the building, peak displacement demand, and the acceleration amplification. Case studies are presented for nonlinear static pushover analysis of walls with distinct bracing schemes to study the influence of bracing configuration on the lateral resistance and deformability of the wall. Moreover, incremental dynamic analysis of building is performed for the derivation of the vulnerability curve correlating the building damage (pull-out of braces) to the base motion severity (PGA). The building resists PGA equal to 0.86 g corresponding to 10% damage probability, showing significant resistance of Dhajji-Dewari structures.

A Bracket‐Stiffened Two‐Planar Overlapped Tubular KT‐Joint for Offshore Jack‐Up Fatigue Analysis

There have been a large number of research programs dedicated to the investigation of stress concentration factor and its parametric design formulae for a variety of uniplanar and multiplanar tubular joints. However, for the multiplanar overlapped tubular joints, the related reports are very limited due to the fact that the combining effect between multiplanarity and brace overlapping is quite complex. In this paper, a novel bracket‐stiffened two‐planar overlapped tubular KT‐joint is proposed by adding two brackets between the upper diagonal and horizontal braces to alleviate the stress concentration at the brace‐to‐chord intersection area. As compared with the original KT‐joint and KT‐joint of larger brace gap, stress concentration reduction and fatigue strength enhancement at the most critical point of the proposed KT‐joint are significant under both axial and in‐plane bending (IPB) loads. The superiority of the proposed KT‐joint is further tested with a simplified fatigue life assessment of offshore jack‐up in field transit condition, when the KT‐joint corresponding to the upper guide level is most critical and fatigue‐sensitive. The obtained results with conservative assumptions may serve as guides or references in civil and offshore engineering practices.

Multi-phase simulation of semi-submersible platform with pencil column using CFD

This paper reports based on a numerical study of multiphase fluid flow through a channel with a semi-submersible platform using computational fluid dynamics (CFD). The present study will be designing and analysing semisubmersible platform with pencil column and without pencil column. The computational fluid dynamics which solves simple differential equations and finite volume method (FVM) will be used. A turbulence model is considered i.e. large eddy simulation (LES). The semi-submersible model is designed as pontoons, columns, horizontal brace, pencil column and deck. The pontoons are horizontal placed stadium shaped structures which are submerged into the water. The columns are structures which connects the deck and pontoons. The horizontal braces are structures which connects the two or more columns which increases the rigidity of the columns. The pencil columns are columns with lesser diameter of about 0.25D which are placed between the columns. The deck are flat surfaces which provides workable area. This paper is a comparison of fluid flow by varying the model i.e. with and without pencil column in the semi-submersible platform. The velocity contours, pressure contours and streamline contours are plotted. The difference in pressure, velocity and streamline flow are tabulated and graphically represented. The percentage difference in pressure and velocity are calculated for structural design for various offshore platforms.

The influence of support condition on 2D frame structure

The offshore structure like jacket, jack-up, gravity and tower can be categorized as a column structure subjected to vertical or horizontal load i.e. the structure is identic with the frame structure. Those structures may be idealized as a frame structure with axial or lateral loads acting on the braces. The present study focuses on the influence of support condition to response of the structure in terms of reactions, displacement and deformations. The support conditions are fixed and hinged at the bottom joint. The load distributions of 10 tonnes are applied at the horizontal brace at the top of the structure. The breadth and depth are 1 m and 1.5 m, respectively. The numerical method is performed to analyze the frame structure. The result obtained by numerical method for three models are compared in therms of support reactions, joint displacement and deformations.

The analysis of 2D frame structure subjected to point load

The offshore structure, like the jacket, jack-up, gravity, and tower, can be categorized as a column structure subjected to vertical or horizontal load, i.e., the structure is identic with the frame structure. Those structures may be idealized as a frame structure with axial or lateral loads acting on the braces. The present study focuses on the analysis of the 2D frame structure subjected to point loads. The support conditions are fixed and hinged at the bottom joint. The point loads of 1 Ton are applied at the vertical and horizontal braces of the frame structure. All point loads are applied in the middle of the brace, either on a horizontal brace or vertical brace. The breadth and depth are 1 m and 1 m, respectively. The result obtained by the numerical method for three models is compared in terms of support reactions, joint displacement, and deformation.

Design of Semi Submersible Platform using Computational Fluid Dynamics

This paper reports based on an experimental study to simulate flow due to irregular fluid flow in a semi-submersible platform using computational fluid dynamics. In this paper we use computational fluid dynamics tools which solve simple differential equations and finite volume method (FVM). A turbulence model is considered i.e. large eddy simulation (LES). The semi-submersible model is considered as pontoons, columns, horizontal brace and deck. The pontoons are horizontal placed stadium shaped structures which are submerged into the water. The columns are structures which connect the deck and pontoons in these model circular columns are considered. The horizontal braces are circular tube-like structures which connect the two or more columns which increases the rigidity of the columns. The deck is a flat surface which provides workable area. This paper is a comparison of fluid flow at different velocity magnitude. The velocity contour, pressure contour and streamline contour are simulated and graphically represented. The numerical simulations are compared with experimental solutions and focus on vicinity of the platform. The difference in pressure, temperature and streamline flow are tabulated and graphically represented. The average percentage difference in temperature and pressure are calculated to be 73% and 128% respectively. Thus, the causation is investigated for the case and several governing parameters are recognized.

Determining the location of sensors for seismic damage detection in steel girder bridges with elastomeric bearings

In planning a bridge health monitoring with minimum sensors for long-term monitoring, it is necessary to accurately predict the bridge behavior including its nonlinearity and identify the damaged bridge components when a strong earthquake strikes. This article presents a methodology for the selection of sensors and their arrangement for detecting seismic damage in an in-service steel plate girder bridge system. In this study, a detailed span-based model was developed for the finite element simulation including the effect of the rubber bearing and piers, and the damage control by the side blocks. The finite element dynamic simulation was carried out with input earthquake acceleration to investigate the seismic behavior and grasp the damageable parts during an earthquake. Based on the results of finite element dynamic simulation, a fault tree analysis was carried out to reveal more about the bridge behavior, the failure modes, and the occurrence of damage. It was found that the side block, the bearing stiffener, and the horizontal bracing on the fixed side of the bridge are most important to be monitored for the evaluation of soundness of a plate girder bridge immediately after an earthquake. Finally, a sensor arrangement for the bridge was proposed based on the analysis results.

Corrugated Box Compression Strength Enhancement

In this study, 5x5x12 single-wall RSC corrugated boxes were strengthened to increase their compression strength using four different methods; horizontal brace, diagonal brace, L-shape corner post, and triangular corner stiffener. All braces are of 2-inch width. Horizontal Brace : Compression strength increased by 9% when the unsupported box height was reduced from 12 inches to 3 inches. Diagonal Brace : Compression strength increased by 8% and 14% for single and double braces, respectively. L-Shape Corner Post : Compression strength increased by 29% and 38% for exterior and interior posts, respectively. Triangular Corner Stiffener : Compression strength increased by 36% when the stiffener depth increased from 0 inch to 9 inches. The interior corner post method was the most effective and most practical.