Diagonal Members Research Articles

Seismic fragility assessment of a super tall building with hybrid control strategy using IDA method

To investigate the interstory drift control effect under different hybrid control schemes using buckling restrained braces (BRB) and viscous dampers (VD), and to study the effect of square root of sum of squares (SRSS) combined intensity measures (IMs) with engineering demand parameters (EDPs) on fragility assessment, incremental dynamic analysis (IDA) based seismic fragility assessment is performed on three numerical models of a super tall building (729 m) in its both structural principal directions. One is the uncontrolled model, the other two are damped models where the BRBs serve as the diagonal member of outrigger truss (BRB outriggers) at the upper part of structure while the improved viscously damper outriggers (IVDOs) are set at the lower location of the building, or conversely. The results suggest that structure can have smaller maximum interstory drift as well as exceeding probabilities if the IVDOs locate at the lower part of structure meanwhile the BRB outriggers are installed at the upper part of structure. Moreover, IDA demonstrates that the SRSS combined IMs and engineering demand parameters (EDPs) may have higher efficiency compared with results from non-combined ones, and the combined EDP limit obtained by the limit in one direction multiply the square root of sum of 1 and λ2, where λ is the ratio of PGA of seismic records input in the two structural principal directions, is also suitable for fragility analysis. Additionally, studies on the fragility analysis using peak ground velocity (PGV) demonstrate that, for tall buildings, PGV is not only suitable for IDA but also works well in fragility analysis based on its high efficiency and reasonable exceeding probabilities.

Experimental modal analysis of diagonal members

Truss bridges are integral part of the transport network, mainly railroads and partially road bridges. The investigated bridge is located in the western part of Slovakia, and it crosses the Vah River. Density of traffic on the bridge is not so high, so the bridge is accessible for repeating dynamic measurements. Many load situations were simulated. Among of them also a case, where one diagonal member was excited by an electromagnetic exciter during the measurements and the influence on other diagonals have been also analyzed. Results of dynamic measurements are shown in this paper in comparison to analytical solution and to FEM calculations.

A Unified Optimal Design Approach for Geometrically Nonlinear Skeletal Dome Structures

In this study, a unified optimal design approach is proposed for the design of skeletal dome structure (SDS). Thus, this study has three objectivities, i) presenting the emergence of proposed design integrity, ii) applying the proposed optimal design approach for the design optimization geometrically nonlinear SDS with both ellipse and sphere-shaped forms considering both the shape, size and topology-related design variables, iii) determining the dominant design criteria in the design of SDS. In this framework, the design of SDS is optimized thereby minimizing its entire weight and joint displacements and maximizing its member forces at the same time. The design constraints are borrowed from the provisions of American Petroleum Institute (API RP2A-LRFD) specification. A multi-objective optimization algorithm (MOA) named Pareto Archived Genetic Algorithm (PAGA), as an optimization tool is integrated by an automatic dome generating tool. Therefore, the novelty of this study comes from being the first attempt to obtain the optimal design in a way of integrating both member and joint-related design constraints by the geometrically nonlinear structural analysis. Consequently, it is displayed that that the proposed optimal design approach facilitates to determine an appropriate optimal design through a tradeoff analysis for designers depending on their preferences. The design concepts concerned with buckling, axial stress, combination of axial & bending, and yielding have the higher dominant effects in the optimal design of SDS. Furthermore, it is also demonstrated that the inclusion of diagonal members into the design of SDS provides a reduction in the violation of dominant design constraints.

Flexural behavior investigation of the CFS truss beams with self-piercing riveted connection

Self-piercing riveted (SPR) connections are gradually being used in cold-formed steel structures due to higher tensile strength, shear strength and connection efficiency compared to those of self- drilling connections. With the purpose of investigating the flexural behavior of truss beams with SPR connections and studying the effects of height and span, as well as diagonal web arrangement, on their flexural stiffness and ultimate bearing capacity, the symmetric vertical static load test was conducted for 5 cold-formed thin-walled truss beam specimens with SPR connections. The finite element software was adopted to simulate the test models, and the more parameters were additionally analyzed. The research indicated that the failure modes of the specimens can be divided into two types: the local strength failure mode occurred when the upper chord flange plate was cracked, the other one occurred when the rivets at joints of truss beams were stripped from the plate. The span-height ratio, spacing of web members, chord thickness and number of rivets had great influence on the flexural stiffness and ultimate bearing capacity of truss beams with SPR connections, while the thickness of web members and the arrangement of diagonal web members had less influence. The truss beam was a simply supported beam with a weak web. A theoretical formula was proposed to calculate the equivalent flexural stiffness of the truss beam with SPR connections based on parametric analysis, and it agreed with the experiment results, so the proposed theoretical formula is valid and can be applied to practical engineering.

Evaluation of Safety Margin on Steel Truss Bridge After-Fracture State

This paper presents fracture critical member identification of steel truss bridge by determining demand to capacity ratio of axial load and linear redundancy analysis of truss bridge. Bridge redundancy evaluation has become crucial in both designing newhighway bridges and repairing or retrofitting old bridges after bridge collapses around the world in recent years. This study aimed to evaluate system redundancy of truss bridge after failure of one critical main truss member. Redundancy analysis is investigated through a case study of four spans continuous steel truss bridge. Finite element (FE) analysis was carried out using SAP 2000 software. In this paper, six cases of diagonal member removal are considered for redundancy analysis. Results from FE analysis showed that the effect of member removal is highest when the damaged truss diagonal member is near the support.

Non – Linear Finite Element Analysis of Mild Steel Gusset Plates

Steel gusset plates / gussets are extensively used in metal buildings and play a crucial role in transfer of forces but yet are most neglected in analysis and design. The inelastic behaviour of mild steel gussets is studied assuming that a diagonal member / brace subjected to a tensile force is connected to the gusset. Non-linear finite element analysis of gussets is performed with the help of a finite element software ANSYS by developing a simple model. Four noded plane stress element is used for meshing. The effects of engineering and true stress-strain curves, yield plateau, type of hardening, angle of inclination of the brace and bolt / bolt hole diameter on the in-elastic stress and strain distribution of steel gussets are discussed.

Disassembling‐Based Structural Damage Detection Using Static Measurement Data

Damage detection methods can be classified into global and local approaches depending on the division of measurement locations in a structure. The former utilizes measurement data at all degrees of freedom (DOFs) for structural damage detection, while the latter utilizes data of members and substructures at a few DOFs. This paper presents a local method to detect damages by disassembling an entire structure into members. The constraint forces acting at the measured DOFs of the disassembled elements at the damaged state, and their internal stresses, are predicted. The proposed method detects locally damaged members of the entire structure by comparing the stress variations before and after damage. The static local damage can be explicitly detected when it is positioned along the constraint load paths. The validity of the proposed method is illustrated through the damage detection of two truss structures, and the disassembling (i.e., local) and global approaches are compared using numerical examples. The numerical applications consider the noise effect and single and multiple damage cases, including vertical, diagonal, and chord members of truss structures.

CHANGES IN THE BEHAVIOR OF THE CHIMPANZEES GOING UP AND DOWN THE TOWER AT SAPPORO MARUYAMA ZOO

Nowadays, zoos are expected to provide facilities that place importance on the living environment of the animals, which should belong in their natural habitats. In a wild rainforest where chimpanzee's live, understories surround tall trees exceeding 20m in height. Chimpanzees, which are semi-arboreal animals, use them when transferring themselves between the treetop and the ground. At the outdoor chimpanzee facility in the Sapporo Maruyama Zoo, ropes, logs, imitation trees were additionally installed as understory substitutes around the tower, that was introduced for environmental enrichment. The objective of this research is to measure the changes in the behavior of the chimpanzees going up and down the tower caused by the additional elements, reveal its causes, and determine what spatial elements around the base of the tower are effective in guiding the animals up the tower. We conducted a behavioral study focusing on the elements used by the chimpanzees during arboreal locomotion on the tower at Sapporo Maruyama Zoo. We separated the tower from its form and its materials into its components, and measured how frequently the tower elements had been used, position of going up and down the tower and trigger elements according to their age. As a result, it was discovered that the imitation tree side platforms, logs and gently inclined ropes that were additionally installed around the tower, were highly influential as they were used by the chimpanzees as an opportunity to move up and down the tower. In particular, by placing a side platform on the left side of the base of the tower, it made it easier to go up and down the tower, increased going up and down the tower from the left, and increased the number of movements by the adults. The logs with gentle inclinations subtending less than 40° with the ground were mainly used for the ascents. Also, the ropes inclined at approximately 25° allowed the intersecting ropes to be used in combination and the usage of the ropes as a whole was increased. Direct climbing of the column ceased, as other handholds were now available in the surrounding area. Moreover, the two ropes connecting the exit from the room to the tower were frequently used as a means of aerial movement instead of using the ground. For the Adult group, there was no change in the basic behavior of climbing the tower by using mainly the columns and the composite materials (beams, piers and decks). However, they began to use the side platforms and logs en route to the column. Also, the object they grasped for support in the beginning changed from the thick pipes to the horizontal ropes. In contrast, the Young group showed a major change in the element usage itself, where they used to descend to the ground via the columns, but now they have changed to jumping off the horizontal ropes using its momentum. From the above, the following four spatial elements around the base of the tower were found to be effective in guiding the animals up the tower: 1. Placing a solid footing by the base of the tower. It should be positioned such that the distance between the footing and the objects on the tower that can be grasped is less than the height of the chimpanzee. 2. Install a slip-resistant diagonal members inclined at less than 40° to the ground with handholds, such as logs with bark. 3. Place ropes arranged so that they intersect with each other. The inclination of the horizontal ropes should be no more than 25°. 4. Install an aerial path to the tower without coming down to the ground.

Behaviour of pultruded GFRP truss system connected using through-bolt with mechanical insert

This paper presents the experimental and analytical studies of double-chorded composite truss system connected using stainless steel through-bolts with mechanical inserts. The composite trusses were assembled using rectangular hollow sections of pultruded glass fibre reinforced polymer (GFRP) where adhesively bonded mechanical inserts were introduced at the vicinity of the joining areas. The trusses were tested under 4-point bending (Load Case 1) and 3-point bending (Load Case 2). From this experimental program, the load-vertical deflection behaviour of the truss, internal forces distribution in the members and joint behaviour were investigated. The pultruded GFRP truss under Load Case 1 was capable of resisting the maximum load capacity of the testing equipment at 450 kN with the lowest factor of safety of 1.10 was attained by the external diagonal members. High axial compression forces experienced by the external diagonal members has exceeded the American pre-standard theoretical joint bearing capacity by 2%, and this was reflected by the minor bearing damage observed on the joints of these members. Meanwhile, the truss under Load Case 2 failed at 160 kN with the continuous top chords ruptured in flexural bending manner. The satisfactory comparisons between the Strand 7 truss model and experimental results demonstrated the validity of the adopted simplified numerical model. Additionally, the theoretical strength limits of pultruded GFRP truss members in tension, compression and flexural according to American pre-standard are in close agreement with the experimental results.

The Effects of Mid-Span Connection Specifications on Compressive Performance of Cross (X) Braces

The aim of this study was assessing the seismic performance of three types of mid-span connections in the cross bracing systems including: the mid-span connection with cover plates, the flanged connections and the braced ductile shear panel (BDSP). For this purpose, the linear buckling and post-buckling behavior of the cross braces with the aforementioned connections having nonlinear geometries and materials were numerically analyzed. The results were compared to the results of the common connection. According to the results, use of the cross braces with mid-span connection together with cover plates and flanged connections due to creating continuity in the mid-span connection, cause coordinated buckling of the discontinuous diagonal members (or so-called second mode buckling) and thereby improved compression performance of the cross braces. In addition, use of the ductile shear panel in the mid-span connection led to more energy dissipation by cross braces and prevented buckling of the diagonal bracing members.

Proposal of design rules for ductile X‐CBFS in the framework of EUROCODE 8

SummaryCross concentrically braced frames (X‐CBFs) are commonly used as primary seismic resisting system, owing to their large lateral stiffness, simplicity of design, and relatively low constructional cost. Current EN 1998‐1 provides design rules theoretically aiming at developing ductile global plastic mechanism, namely enforcing plastic deformations in the diagonal members, while the remaining structural members and connections should elastically behave. However, as widely demonstrated by many existing studies, the design and the corresponding seismic performance of EC8‐compliant X‐CBFs are generally affected by several criticisms, eg, difficulties in sizing of diagonal members, massive and non‐economical structures, and poor seismic behavior. In light of these considerations, the research activity presented in this paper is addressed to revise the design rules and requirements given EN 1998‐1 for X‐CBFs to simplify the design process and to improve the ductility and the dissipative capacity of this structural system. Hence, design rules are proposed for the next version of EN 1998‐1 and numerically validated by means of nonlinear dynamic analyses.

An iterated IRS technique for cross-sectional damage modelling and identification in beams using limited sensors measurement

ABSTRACTThis paper presents an effective method for cross-sectional damage localization and quantification in beams. First, a new strategy is suggested for cross-sectional damage modelling by means of Iterated Improved Reduction System (IIRS) approach. Then, a novel damage localization index is proposed employing Grey System Theory (GST) as a geometrical criterion for quantifying the amount of correlation between vectors of the calculated curvatures for the diagonal members of the flexibility matrices in the damaged and undamaged states. Since the method employs only the modal data of the translational degrees of freedom, it can be interpreted as damage identification method by utilizing incomplete modal data or installing a limited number of sensors. After detecting the damage location, to estimate the exact parameters of the cross-sectional damage, the problem is defined as a finite element model-updating problem which is solved with a new evolutionary optimization approach named Imperialist Competitive Algorithm (ICA). The applicability of the method is demonstrated by studying different damage patterns on two numerical examples of beams. In addition, its robustness is investigated in the presence of random noises and modelling errors. Obtained results emphasize the high accuracy and promising performance of the method, especially when noisy incomplete modal data are used.

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.

Enhancing Local Buckling Behavior of SHS Braces Using GFRP and CFRP Wrap

AbstractDuring earthquakes, diagonal members of concentrically braced frames are meant to dissipate hysteretic energy through their postbuckling performance. However, crack formation at the locatio...

Mutual effect of geometric modifications and diagrid structure on structural optimization of tall buildings

ABSTRACTStructural efficiency and flexibility in architectural planning have made diagrid structural system so popular among engineers and architects, currently. Since considering architectural and structural parameters can help architects and engineers to have more efficient buildings the focus of this research is to study the effect of both different geometric base and top plans configurations of tall building and the angle of diagrid structure to design efficient tall buildings with respect to two objectives: the total weight of structural elements per unit area and horizontal displacement of top floor (both minimized). To this aim, 64 parametric models with various cross-sectional shapes and 180 m height are generated by randomly increasing the number of sides at the base and top plans. The generated models are developed for varying angle of diagonal members. Rhino software and its plug-in Grasshopper are used for modelling and Grasshopper's plug-in called Karamba is used for structural analysis. The optimal models are resulted by means of genetic algorithm-based optimization. Ultimately, it is found that the optimum bound for diagrid angle is between 53° and 70° and if the number of polygonal cross-sections goes up, the efficiency of the buildings with diagrids that have the optimum diagonal angles increases.

A new type of truss joint for prevention of progressive collapse

This paper presents a study on a new type of truss joint (Pinned-Slidable or PS joint) that is designed to maximize the function of catenary action upon a sudden member removal. The basic idea for a PS joint is such that it is fixed on the bottom chord without sliding under the design load, but can slide along the bottom chord to help distribute the unbalanced tensile forces that the catenary action generates on different bottom chord members. The sliding resistance of this joint is provided by the friction generated by the preloaded bolts and the shear resistance of a locking rod, which can be designed according to the proposed design schemes. A Warren truss with PS joints as the bottom joints (Truss-PSJ) has been designed and tested under a scenario of a sudden removal of one of its diagonal members, and the response of the structure is compared with that of an identical truss model except for its non-slidable joints (truss-PJ). Results show that significant catenary action develops in the bottom chord of the remaining structure in the process of establishing a new equilibrium state after the member removal, and the catenary action tends to generate much larger tensile forces in the bottom chord members in the mid-span than in the neighboring bottom chord members, leading to the sliding of a PS joint. By comparing the test results of truss-PSJ with those of its counterpart truss-PJ, the benefits of the PS joints have been clearly demonstrated. The sliding of the PS joint not only releases the excessive unbalanced forces between neighboring members and thus enables a fuller development of the catenary action, but also facilitates the adaptation of the remaining structure towards a new balanced state with a near-optimal deformation shape. A finite element analysis has also been conducted to confirm the above experimental observations, and to demonstrate the performance of PS joints under other progressive collapse scenarios. Furthermore, a method for determining the sliding resistance of PS joints is also proposed.

Dynamic analysis of temporary steel grandstand equipped with different types of bracing system

In the paper, behaviour of a temporary steel grandstand equipped with two different types of bracing system has been analysed through the numerical study. A typical solution concerning application of a diagonal tubular members has been compared with elements proposed by authors and called polymer dampers. A polymer element consists of two L-shape steel members bonded with polymer mass. The aim of the paper is to verify the effectiveness of polymer dampers in reduction of vibrations of temporary metal grandstands subjected to dynamic loads induced by spectators. The results of the study show that the response of structure equipped with two analysed bracing systems is different variable. The application of the polymer dampers results in substantial reduction in structural vibrations. Moreover, the decrease in values of accelerations of the grandstand with polymer dampers allows to maintain comfort of spectators at an acceptable level.

Lateral Displacement and Shear Lag Effect of Combination of Diagrid-Frame

Diagrid system, which is the portmanteau of diagonal grid member, is an exterior lateral load resisting system for tall building that has gained a wide acceptance in the design of tall buildings. There is abundance of researches that studied the efficiency of diagrid systems, which are constructed from the ground level to the top of the buildings in resisting the lateral load. Nevertheless, no study had been performed on the effectiveness of the diagrid that is constructed above other tall building systems despite the existence of a few buildings in the world that employ such system. The objective of this research is to understand the behavior of the lateral displacement and shear lag effect due to wind load when the diagrid structure is constructed above a frame. Models of 60-story buildings with a footprint of 36m x 36m were analyzed by using Staad.Pro software. The level where the diagrid members started was altered. The lateral displacement was reduced to 60.6 percent and 41 percent of the lateral displacement of a building with full frame system when the combination of frame-diagrid that had the diagrid started at Level 1 and Level 45, respectively were employed. Furthermore, the shear lag ratio was reduced from 1.7 to 1.3 when the level where the diagrid started was increased from Level 1 to Level 45.

Optimal Design of Hanging Truss Having SMA Wires (From Vibration Isolation and Attenuation Viewpoints)

A column-type truss structure is generally unstable without diagonal bracing members. It is, however, mechanically stable in so-called hanging configuration due to the effect of gravitational force. This kind of structure can isolate an apparatus installed at its tip end from the influence of the vibration of the support ceiling, where the hanging truss structure is placed. The relationship between the stress and strain of the shape memory alloy (SMA) material in relatively high temperature condition has a hysteretic loop, which can be adopted for the purpose of vibration attenuation and isolation. A truss structure with bracing SMA wires in hanging configuration is expected to possess both of the abilities of vibration isolation and attenuation. In this study, optimal placements of SMA wires are obtained by a GA-based approach from the vibration isolation and attenuation points of view under the constraint condition of the number of the SMA wires. Crossover and mutation operators in order to deal with the constraint condition of the number of SMA wire members are proposed. The non-dominated Pareto fronts are obtained for the cases of various numbers of SMA wire members. On the basis of the calculations, it has been confirmed that the number and the placement of the SMA wires are significant factors on the effects of vibration isolation and attenuation. Most of the optimal configurations have one common feature that the SMA wires are distributed close to the middle of the hanging truss structures and there are few SMA wires at the truss units near the support ceiling as well as the peripheral end. The placements of SMA wires in optimal solutions show, however, a tendency of decentralization in the case of emphasis on vibration isolation.

Vibration-Based Health Monitoring of an Existing Truss Bridge Using Energy-Based Damping Evaluation

This paper proposes an analytical framework for vibration-based structural health monitoring (SHM) by introducing an energy-based damping evaluation (EBDE). The damage detection by the proposed EBDE was carried out by estimating the contribution of modal damping ratios from different structural elements utilizing experimentally identified modal damping ratios, and estimating modal strain and modal potential energies from an updated finite-element (FE) model of the structure under consideration. Model updating was performed using modal frequencies and mode shapes that are generally not sensitive to local damage. The advantage of using damping as a damage indicator is that the damping change in global modes affected by the local damage can be identified with a small number of sensors. A previous study reported that the studied bridge with damage at the local diagonal member showed a significant increase in the damping of global vibration mode of the structure. The present study utilized the EBDE to identify the cause of the modal damping increase by observing the change in the contribution from different structural elements on the modal damping ratios.