Steel Braces Research Articles

Nonlinear behaviour of reinforced concrete moment resisting frame with steel brace

Nonlinear behaviour of reinforced concrete moment resisting frame with steel brace

Performance-Based Design of RC Structures Subjected to Seismic Load Using a Hybrid Retrofitting Method with Friction Damper and Steel Bracing

Performance-Based Design of RC Structures Subjected to Seismic Load Using a Hybrid Retrofitting Method with Friction Damper and Steel Bracing

Macromodeling Approach and Robustness Enhancement Strategies for Steel Frame Buildings with Composite Slabs against Column Loss

This study presents a numerical assessment of the behavior of seismically designed steel frame buildings against ground floor column loss. In the designed prototype buildings, moment frames with beam-to-column rigid connections and concentric X-bracing frames resist the lateral force, whereas the steel-concrete composite floor slabs resist the gravity load. Macromodels are used to capture the building response when removing ground floor columns. The macromodels are built with a reduced modeling approach, in which the concrete damage and the local steel fracture behavior are accurately considered. The macromodeling approach is calibrated by high-fidelity models and validated by composite floor test. The validated macromodels are used to investigate the effect of column loss location, total number of floors, floor slab, beam-to-column connection type, adjacent span, and steel brace on the collapse resistance of prototype buildings. To account for sudden column failure, an energy-based approach is used to convert the quasi-static response curves to dynamic response curves. The structural robustness is derived by comparing each column failure case’s dynamic ultimate capacities with corresponding design requirements. Structural robustness enhancement strategies for steel frame buildings under progressive collapse scenarios are summarized and discussed. Moreover, a retrofitted moment-resisting connection with steel strands is proposed to enhance the steel frame buildings’ robustness by providing a second line of defense.

Performance evaluation and strengthening of reinforced concrete buildings

In view of the past earthquakes, it is stated that several structures are located in active seismic zones around the world. So, improvement of the earthquake performance levels of the existing buildings by using various strengthening methods has been the major interest in structural engineering. Non-linear analysis procedures that are defined in several seismic codes exhibit reliable results in the evaluation of seismic performances of existing buildings. In this study, seismic performances of three, five and eight storey existing and strengthened reinforced concrete buildings having the common floor plan, material and section properties of the structural members are investigated according to Turkish Building Earthquake Code-2018 and American Standard, ASCE. To obtain the earthquake performance results of reinforced concrete buildings, displacement demands of the buildings have been obtained and utilized in nonlinear analyses. SAP2000 structural analysis software is used in the solutions. The determined strengthening techniques are provided by adding concentric steel bracing members to existing reinforced concrete buildings and jacketing of the determined columns. As a result of non-linear analyses applied to the existing and strengthened buildings, damage situations of the structural members are determined, seismic performances of the buildings are evaluated according to both codes and the results are interpreted in the end.

Comparative analysis of earth quake resistant building design by considering bracings and shear wall system in ETABS software

Earthquakes are one of nature's most prominent risks to life on this planet and have decimated incalculable urban areas and towns on for all intents and purposes each landmass. Earth quack resistant structure is one of the most important concept in structural engineering. According to building design codes, earth quake resistant is depending upon the seismic zones. As per IS code 1893:2015 code seismic zones are classified in to four types they are Zone V, Zone IV, Zone III and Zone II. Everyday new procedures are being produced for the advancement of living arrangements financially, rapidly and satisfying the prerequisites of the gathering specialists and creators do the crease work, arranging and design, and so on, of the developments. The bracing systems and shear wall systems are generally used for designing the earth resistant structures, due to its simple construction methods and easy to install at the site. Both bracing systems and shear wall methods reduces the deflection of building as per the considerations. In the present study a G + 12 building is modeled by using ETABS Software and analysis is carried out by using Response spectrum analysis. The results like storey drift, storey shear, storey bending, time period and frequency were compared for building models made with steel bracings and shear wall systems.

Development and experimental study of a novel steel brace with load-bearing adjustable capacity utilizing the buckling behavior of partial steel plates

To regulate the seismic failure mode of a structure, this paper proposes a novel steel brace with load-bearing adjustable capacity (NSB-LBAC) utilizing the buckling behavior of partial steel plates. The NSB-LBAC comprises an outer steel tube, a slidable force-transmission steel tube, two load-bearing adjustable steel plates (LBASPs), two force-transmission components, and connectors. The LBASP with buckling and buckling-restrained segments was designed to adjust the nonlinear load bearing of the NSB-LBAC. The nonlinear load-bearing capacity can be adjusted by controlling the proportion of buckling and buckling-restrained segments. Considering the influences of the adjustable area ratio and length of the un-strengthened zone, pseudo-static experiments were conducted on five NSB-LBAC specimens to investigate their mechanical properties, load-bearing capacity, and energy dissipation capacity. The experimental results demonstrated that the proposed NSB-LBAC can achieve a load-bearing adjustable capacity by utilizing the buckling behavior of partial steel plates. The increased adjustable area ratio and length of the un-strengthened zone can reduce the post-buckling load-bearing capacity, and increased adjustable area ratio can retard the growth of the post-buckling load-bearing capacity. The increased length of the un-strengthened zone can increase the ductility of the NSB-LBAC. The proposed NSB-LBAC can provide an excellent energy dissipation capacity, and the increase in the adjustable area ratio can increase the energy dissipation capacity of the NSB-LBAC. A theoretical analysis model considering the buckling behavior of partial steel plates is proposed to evaluate the initial stiffness, yield load, and ultimate load of the NSB-LBAC.

Seismic performance of suspended‐floor structures with viscous dampers considering acceptable interstory drift

SummaryNumerical studies of suspended‐floor structures were conducted, and viscous dampers were applied to improve their seismic performances. The following issues were analyzed under 20 earthquake records: seismic responses of the primary structure and suspended floors, the distributions of the damping coefficient c0, and the interstory stiffness of the suspended floors. There was a significant reduction in the roof drift and the base shear force of the cores after replacing the steel bars with viscous dampers. The suspended‐floor structures with viscous dampers exhibited an optimal c0. The suspended‐floor structure with a triangular distribution of c0 showed a smaller seismic response than the one with a uniform distribution of c0. Under the design‐based earthquake, there was complete damage of nonstructural components in the y‐direction. Hence, applications of diagonal steel braces within the 1st to 10th floors were suggested to increase the lateral stiffness of the suspended floors in the y‐direction. The application of diagonal steel braces reduced the story drift Sd of the suspended floors, resulting in slight damage to nonstructural components under the design basis earthquake (DBE) hazard level. However, the roof floor, which contains electrical and mechanical components, exhibited an increase in Sd after the application of the diagonal steel braces. With increasing stiffness of the diagonal brace, the story drift profile of the suspended floors tended to be uniform, and the suspended‐floor structures with the uniform distribution of c0 exhibited seismic performances closer to those of the suspended‐floor structures with the triangular distribution of c0.

Full-Scale Blast Tests on a Conventionally Designed Three-Story Steel Braced Frame with Composite Floor Slabs

This paper summarizes the findings of two full-scale blasts tests on a steel braced frame structure with composite floor slabs, which are representative of a typical office building. The aim of this research study was to experimentally characterize the behavior of conventionally designed steel braced frames to blast loads when enclosed with conventional and blast-resistant façade. The two tests involved a three-story, steel braced frame with concentrical steel braces, which are designed to resist typical gravity and wind loads without design provisions for blast or earthquake loads. During the first blast test, the structure was enclosed with a typical, non-blast-resistant, curtainwall façade, and the steel frame sustained minimal damage. For the second blast test, the structure was enclosed with a blast-resistant façade, which resulted in higher damage levels with some brace connections rupturing, but the building did not collapse. Observations from the test program indicate the appreciable reserved capacity of steel brace frame structures to resist blast loads.

SHEAR STRENGTH OF JOINT METHODS FOR SEISMIC RETROFITTING USING STEEL SHEAR-KEY OF FRUSTOCONICAL SHAPE AND POST-INSTALLED ANCHOR

To strengthen reinforced concrete structures against seismic events, design methods are being established to fit the interiors of existing structures with steel braces or shear walls and to retrofit existing structures with steel braces on the exterior of existing frames for seismic protection. For example, indirect connections that use post-installed anchors are frequently employed in steel-braced frames for seismic retrofits, and many post-installed anchors are required for each existing structure. The connection between the existing structures and reinforcement elements in the seismic retrofitting of concrete construction must be effective in distributing stress. If the strength of the connection is not adequate and if the details are not properly designed, the structure as a whole is not likely to display effective seismic performance. Therefore, we proposed a new method that uses shear connecters with a steel shear key in a frustoconical shape and post-installed anchors for connecting existing concrete to extended concrete. We call this shear connecter the “funnel-shaped post-installed anchor.” In a former study, experiments and non-linear finite element method analysis on the strengthening method that used funnel-shaped post-installed anchors reported that funnel-shaped post-installed anchors with a 45-degree shear key improved shear strength compared with keys with other shapes. However, no shear strength formula has been established for this new type of shear connecter.

Effects of Steel Braces on Robustness of Steel Frames against Progressive Collapse

External installation of steel braces is an effective approach to increase the lateral load resistance of steel moment-resisting frames. However, the effects of existence of steel braces on the robustness of steel moment-resisting frames to resist progressive collapse is still not clear because little study has been carried out. To fill this gap, in this paper, six multistory steel moment-resisting subframes (three bare frames and three braced frames) were fabricated and tested. Test results indicated that the specimen with reduced beam section in the connection zone performed best among three types of connections due to the guaranteed formation of plastic hinges at the location of reduced section and avoiding brittle fracture of weld at the connection. Experimental results proved that steel braces could increase the load-resisting capacity by 45.1% and 83.9% of the frame with weld connection and end plate connection, respectively. The gusset plate restricted the rotation of the plastic hinges in the second story of the braced frames with V-shaped bracing, which decreased its deformation capacity and degraded its catenary action capacity. Actually, the ultimate load of the braced frames with V-shaped bracing is only 87.5% of that of the counterpart without any braces. Because the compressive braces were severely buckled before the displacement reached 0.4% of the beam span, it had little effect on yield load but increased the initial stiffness of the bare frames. Thus, a majority of the benefits of the bracing system were attributed to the tensile braces. Moreover, the analytical results evaluated the differences in load resistance and development of load-resisting mechanisms in different stories. Furthermore, the contribution of compressive and tensile braces was decomposed individually by analytical analysis.

Investigation of the effects of different central steel brace type on nodal point connection detail and building behaviour

High strength and ductility properties of steel structures have been the reason for the preference against earthquake effects. However, it has observed that significant damages occurred in particularly the nodal point connection of the steel structures in the investigations made after the earthquakes. Therefore, it is very important to know the effect of different central steel brace and nodal point connection type on steel structure behavior. The main purpose of this study is to comparatively examine the effects on the behavior of steel structures of the different central braced types and nodal point connection detail. The findings obtained from structural analyses reveal that different central steel brace members contribute positively to the behavior of steel structures. This result shows that central steel braced that increase the performance of steel structures are very important. In Turkey, particularly in terms of the safety and performance of the steel structures to be constructed in earthquake zones is proposed to prefer steel structural systems with bidirectional central steel braces.

Development of multiutility wheelbarrow

Wheelbarrow is a simple machine a large open container to move things, which belong to the second-class lever. This is because the load or resistance is placed between the effort and the fulcrum. Wheelbarrow can be used as farm equipment, industrial equipment, among others. A wheelbarrow might consists of a tray or bed composed of steel, wood, or plastic. A steel brace attaches this bed to steel support legs and to a steel or plastic wheel, with a rubber tire around. In two- or four-wheeled models, the wheels may be similar to bicycle tires, complete with inner tubes. Materials used in the construction of the wheelbarrow. Our goal is to innovate a product that is useful on everyday basis but also turns into a safety equipment when needed. With extensive research we have designed a wheelbarrow that is multipurpose in nature. It can be used as a normal wheelbarrow on the day-to-day activities and as a floatation device to carry load and children in terms of floods. Our process included everything from research into the selection of materials into the most optimum design that would be feasible both technically and economically. The analysis has been done by using Ansys. We also tuned the ergonomics of the wheelbarrow so that it is easy in operation which can be used on day-to-day basis.

Fatigue behaviour of non-welded wrapped composite joints for steel hollow sections in axial load experiments

Design and execution of fatigue load dominated circular hollow section (CHS) multi-membered structures, such as offshore jacket and floating structures for wind turbines, truss bridges, etc., is hinged on fatigue performance of critical welded joints. An innovative jointing technology of wrapped composite joint connects steel hollow sections by direct bonding through a fibre reinforced polymer composite wrap, which completely avoids welding and therefore has superior fatigue performance than welded joints. In this study first results on fatigue performance of the wrapped composite joints is presented. Tensile cyclic loading tests on wrapped composite X-joint specimens were carried out to characterise their fatigue performance under different constant amplitude load ranges and compare it to equivalent welded joints. In addition, the influence of surface roughness of steel tubes and re-testing (load history) on fatigue performance of wrapped composite joints, as well as the influence of fatigue loading on residual static resistance was investigated in experiments. Preliminary S-N curves of wrapped composite joints are established. The tests results showed that X45 wrapped composite joints exhibited steadier stiffness degradation and 10–100 times longer fatigue life than their welded equivalents. Through 3D DIC surface strain measurements and post-failure microscopic insights to cut specimens, different failure modes including de-bonding at glass fibre composite-to-steel interface, delamination/fracture of the composite layers and fracture of steel brace are distinguished. The relationship between joint stiffness degradation rates, crack propagation rates and nominal stress ranges in the brace are established, based on which a preliminary fatigue life prediction of wrapped composite joints can be made. The re-tested specimens exhibited superior fatigue performance than virgin ones, while specimens with poor steel surface roughness showed worse fatigue performance. After fatigue loading with 40% of stiffness degradation, the specimens were found to still have the potential to sustain its original static resistance.

Optimization of VEDs for Vibration Control of Transmission Line Tower

This paper investigates the optimization of viscoelastic dampers (VEDs) for vibration control of a transmission line tower. Considering the stiffness of the steel brace connected to a VED, the mechanical model of the VED-brace system was established. Subsequently, the additional modal damping ratio of the transmission line tower attached with VEDs was obtained analytically. Furthermore, the finite element model of a two-circuit transmission line tower with VEDs was built in ANSYS software, and the influences of installation positions and parameters of VEDs on the additional modal damping ratio were clarified. In addition, the control performance of VEDs on the transmission line tower subjected to wind excitations was emphatically illustrated. The results show that the stiffness of the steel brace connected to a VED has a significant effect on the maximum additional modal damping ratio of the VED-brace system provided for the transmission line tower and the optimal parameters of the VED. Meanwhile, the installation positions of VEDs dramatically influence the additional modal damping ratio. Moreover, the increase of the brace stiffness and the loss factor is beneficial to improve the control performance of VEDs. Besides that, the VEDs present superior control performance on the top displacement of the transmission line tower as well as the transverse bending vibration energy.

Effective buckling length of frames with tapered columns and partially tapered beams

This paper presents stability analysis of steel frames composed of linearly tapered columns and partially tapered restraining beams. In the first part of the stability analysis, closed-form equations for the bending stiffness of the symmetrical and unsymmetrical partially tapered restraining beam are derived and presented in form of design charts. Subsequently, slope deflection equations of linearly tapered column subjected to axial compressive load are then assembled along with the bending stiffness equations of partially tapered beams to determine the elastic critical load and the effective buckling length factor for non-sway and sway steel frames. Numerical examples and efficient design charts are presented for several braced and unbraced steel frames. Moreover, the effect of gravity loads acting on leaning columns connected to sway frames is investigated. Based on this investigation it is concluded that correction of effective buckling length factor based on story buckling concept can be extended to cover steel frames with tapered column as well.

EXPERIMENTAL STUDY ON SEISMIC PERFORMANCE OF ENERGY DISSIPATION AND POSITION LIMITATION STEEL BRACE AND STRUCTURE SEISMIC VULNERABILITY ANALYSIS

A kind of energy dissipation and position limitation type steel brace is proposed to improve the seismic performance of a building structure. Five steel braces are designed, and the limitation displacement, limitation block number, steel core section size and length are chosen as the design parameters. Based on the test study, the characteristics including the failure mode, hysteresis loops behavior, skeleton curves, and stiffness are demonstrated. The seismic collapse resistance of steel braced frame structures is evaluated through IDA analysis. The results show that: the steel brace structure is reasonable with stable hysteretic performance, and the position limitation block could play a limiting role and provide greater additional stiffness. The number and section size of the position limitation block and the weld stiffness of the joint surface with the steel core affect the lifting degree of the additional stiffness. The calculation results of the stiffness formulas presented are in a good agreement with the experimental values, which can provide a reference for the practical design of steel braces. The collapse reserve coefficient of this type of steel braces with position limitation blocks is increased, beneficial to improve the collapse resistance of soft first storey building.

Evaluating the effect of Buckling-Restrained Braces in Steel Buildings against Progressive failure using Different Simulation Strategies

Ignoring the primary damage to structural components due to blast load or fire is the alternate load path (APM) method's weakness in progressive failure analysis. The new technique used in this study examines the structure's more realistic responses by considering the initial cause of the failure. Also, buckling-restrained braces (BRBs) are applied to diminish the potential for progressive failure in braced steel buildings. Variables include the type of primary local loading (APM, blast loading, and heat caused by fire), the position of column removal in the plan (inner and outer frame), the type of brace (BRB and CB), and the number of stories (3, 5, and 8 stories). The buildings were simulated using ABAQUS. The results showed that BRBs in steel buildings under blast load, compared to conventional braces, reduce the potential of progressive failure. The use of BRBs provides much more energy absorption than conventional bracing systems due to brace buckling prevention.

Calculation Method of Underground Passage Excavation on Interactive Effects among Pipe-Roof, Steel Bracing and Foundation Soil

The ultra-shallow buried excavation technology, utilizing pipe-roof steel arches as main supporting structure, has broad application prospects. Current mainstream pipe-roof design schemes often adopt simple beam theory or engineering analogy methods, which do not take into account the cumulative deformation and have high engineering disaster risk. Based on the beam Winkler model of elastic foundation, this paper studies the method on interactive effects among pipe-roof, steel bracing and foundation soil. The calculation model of the ultra-shallow buried pipe-roof and steel bracing is established with theoretical derivation. And a new supporting design method of ultra-shallow buried excavation under interactive effects is proposed. Firstly, an optimal method for determining the elasticity coefficient of steel arch and foundation soil is put forward on interactive effects among pipe-roof, steel bracing and foundation. Secondly, considering the enhancement effect of concrete wall, a procedure of determining the elasticity coefficient of fulcrum is described. That is, the first steel arch, which is adjacent to underground passage tunnel face, returns to the 1.5H (H is the height of the hole) range as an enhanced transition section, and the elasticity coefficient of fulcrum varies linearly with its position. Furthermore, the key issue is the deformation of the inlet section increases to a stable level in a certain range, while the ground settlement does not exceed the threshold. The selection of pipe-roof is controlled by calculated deformation. If the deformation meets the requirements, the internal force will be far enough to meet the requirements. Only two sections need to be considered when calculating the ultra-shallow buried underground passage, the entrances 2.0H and the central across section. Finally, the accuracy of the interactive effects calculated method is validated by using the measured data of a practical example.

Dynamic response of multi-story buckling-restrained braced steel frames with different β values

The average shear-bearing ratio (β) of buckling restrained brace (BRB) is a key parameter, affecting the seismic performance of buckling restrained braced steel frames (BRBF). In order to determine the dynamic response of multi-story BRBF with different β values, two kinds of structural models are established, one is with the rigid connection of beam-column joints, and the other model has both hinged and rigid joints. The nonlinear time-history analysis of multi-story BRBF structures are carried out by selecting the seismic waves with predominant period close to the first mode period of each research model, and the seismic waves that are significantly different from it. The influence of β on the shear displacement, bending displacement and vibration mode of the structure are revealed: when β ≤ 30%, the story drift of multi-story BRBF structure is mainly shear deformation and the first vibration mode is predominant. When β increases, the bending deformation of the story drift increases. The second vibration mode of the structure is predominant when β ≈ 90%. It is suggested that the equivalent seismic force of multi-story BRBF structure with β > 30% should not be calculated by the base shear force method.

Theoretical analysis and optimization of toggle-brace damper for cable tray system

The cable tray system, one type of non-structural components, may suffer severe damage and even fall in case of earthquakes, causing interruptions to post-earthquake operations and even injuries or casualties. This paper introduces a toggle-brace damper (TBD) into the cable tray system to control its seismic response and damage. However, owing to the large deformation/rotation effect in the TBD equipped cable tray system, the traditional design method based on small deformation assumption is no longer applicable. The new deformation calculations of suspension frame and TBD subjected to displacement loading are established combining the optimization technique and the geometry relationship, respectively. After then, an optimization design method for connecting location of the damper brace is proposed, considering the installation errors, deformation constraints, and loading process. With the aid of numerical analysis, it is found that the large deformation effect and in-plane installation errors have considerable influence on the damping magnification function. Compared with typical seismic resistant elements such as the steel brace, diagonal- and chevron-brace damper, the proposed optimal TBD can dissipate more energy and effectively suppress the vibration of cable tray system.