Horizontal Bracing Research Articles

Seismic performance of elevated steel silos during Van earthquake, October 23, 2011

Silos are commonly used industrial structures to store dry/granular materials like cement or wheat. A typical silo consists of a vertical steel tank supported by a braced steel frame which rests on concrete support. Due to unloading purposes, the tank is generally located at an elevated position. This makes the structure vulnerable to axial loads in columns due to excessive overturning moments generated at the base of the structure. During the October 23, 2011 Van earthquake in Turkey, many silos collapsed either due to column buckling or foundation problems. In this paper, the field observations regarding the seismic performance of silos after the Van earthquake are first summarized. Then, the seismic performances of two steel-elevated silos located in the earthquake region are studied. One of the silos survived the earthquake by some minor damages in the form of buckling (at bottom horizontal brace) and spalling of concrete support, while the other silo remained undamaged. Nonlinear dynamic time history analyses are performed to evaluate the seismic performances of both silos. As the input ground motion, the recorded ground motion from a temporary aftershock station (about 2 km away from the silos) in the second earthquake is used. Analyses indicate that design and construction quality of elevated silos determine the seismic performance. Finally, recommendations are given to improve the seismic performance of new constructions.

Effects of Braces on Progressive Collapse Resistance of Steel Frame

In order to carry on the progressive collapse analysis more properly, nonlinear-dynamic analysis method is used to analyze five-storey of steel frame structure. Four structure schemes have been established, namely frames, frames with horizontal braces, frames with vertical braces and frames with horizontal cross braces. According to analyzing with different position of failure column on the first floor, the curves of displacement-time of column failure point and axial force of failure column’s neighboring are obtained. The results indicate that horizontal braces can reduce the vertical displacement above damaged column and the axial force of the columns on the first floor evidently. The vertical displacement of horizontal cross braces is less than which of horizontal braces.

Influence of pallets on the behaviour and design of steel drive-in racks

This paper analyses the influence of horizontal bracing restraints provided by the friction between pallet bases and rail beams on the static behaviour and design of steel drive-in storage racks. The pallet bracing restraints are shown to significantly influence the structural behaviour of the rack, and their effect on the bending moment distribution of the uprights is studied in the paper. The 2D single upright model proposed by Godley is improved in this study by including the restraints provided by the plan flexural stiffness of the rail beams and the friction between the pallets and rail beams. The improved 2D model was found to accurately reproduce the bending moment distributions obtained using 3D advanced finite element analysis. The 2D single upright model is used to analyse 36 drive-in racks under various load case combinations. The paper evaluates the influence of the pallet bracing restraints on the ultimate capacity of drive-in racks, clarifies the loading pattern(s) governing the structural design and determines the friction coefficient, or strength of a restraining device, required to prevent the pallets from sliding. It is shown that while restraints from pallets could potentially be considered in design, they would not lead to more economic structural solutions.

Study on mid-height horizontal bracing forces considering random initial geometric imperfections

In order to investigate the different mid-height horizontal bracing forces of column–bracing system between pin-ended column base and fixed-ended column base, a large number of column–bracing systems with pin-ended column base and fixed-ended column base have been modeled and analyzed using finite element method, in which the random combination of the initial geometric imperfections between columns and braces was well considered by the Monte Carlo method. Based on the above comparative study, the probability density function of mid-height horizontal bracing forces was found through probability statistics and the design bracing forces were also obtained. It is founded that the buckling mode of columns for pin-ended column base is three half-waves of bending while the buckling mode of columns for fixed-ended column base is two half-waves of bending, so that the ultimate load-carrying capacity and the mid-height horizontal bracing forces of column–bracing systems with pin-ended column base are higher than those of column–bracing systems with fixed-ended column base, and the relative high ultimate load-carrying capacity of the former more significantly increases its mid-height horizontal bracing forces. The results also indicate that random combination of the initial geometric imperfections between columns and braces leads to the randomness of mid-height horizontal bracing forces in compression or in tension, so that the design bracing forces can be reasonably reduced which are smaller than those stipulated in GB50017-2003, Eurocode3-1992 and AS4100-1998. Moreover, practical design formulas of mid-height horizontal bracing forces are proposed.

Design Method of a New Type of Expansive Stressed Grouted Clamp

Considering the different mechanism of self-stress formation, a new type of structure was proposed for expansive grouted clamp, which is used for underwater repair on steel tubular. Since the structure is changed totally, the corresponding design method should be modified. This paper summarizes a design method of the new type of expansive stressed grouted clamp and sorts out a set of practical design procedure for the new structure. The core principles of the design method are based on the checks on slip capacity, member crushing and structural strength, associated with the experiment data and previous design experience as reference. An example of such clamp design for repairing a horizontal brace of a jacket platform is also introduced to describe how this method works.

Design Method of Horizontal Braces Unlocated at Middle of Columns with Fixed-Ended Column Base

A large number of column-bracing systems for the horizontal braces unlocated at middle of columns with fixed-ended column base were modeled and analyzed by second-order analysis using finite element method, in which the random combination of the initial imperfections between columns and horizontal braces was well considered by Monte Carlo method. According to the analysis results, two kinds of instability modes of column-bracing system have been found, probability density function of the horizontal bracing forces unlocated at middle of columns with fixed-ended column base is established based on probability statistics, and the design formula of horizontal braces unlocated at middle of columns are also proposed.

Damage Detection for Offshore Platforms Based on Modal Redundancy Index of Damaged Member

According to the phenomenon that global damage detection of jacket platform is influenced by structure redundancy of damaged member, the concept of modal redundancy index (MRI) of damaged member is proposed. Through numerical simulation by means of mode strain energy method, the way that MRI of damaged members in different types and positions changed was studied, as well as the relationship between MRI and global damage detection. The numerical simulation result demonstrated that when MRI of pile element is less than 2.1×103, damage can be detected; when MRI of slanted brace element is less than 1.5×105, damage can be detected; when MRI of horizontal brace element is more than 5.8×105, damage cannot be detected. Therefore MRI can be a reference index in engineering application of global damage detection of offshore platforms.

Optimization Design of the Crane Girder Based on Adaptive Genetic Algorithm

With taking weight of single main beam of gantry crane as objective function, and taking main beam upper & lower cored, diagonal & horizontal bracing, and width & weight as design variable, this essay adopted population diversity adaptive genetic algorithm to optimize its structure and improved program design through MATLAB. This algorithm could accelerate convergence speed, which make much it easier to realize comprehensive optimal solution, since it effectively avoided weakness of basic genetic algorithm, such as partial optimal solution, prematurity and being lack of continuity, etc.

Load Capacities of Single-Layer Shoring Systems: An Experimental Study

This investigation elucidates the load capacities of wooden shores and adjustable steel tube shores that are commonly used in construction. A series of loading tests was performed based on actual setups used on construction sites. Research results reveal that the load capacity of an isolated wooden or an adjustable steel tube shore declines as its length increases, and the load capacity of adjustable steel tube shores greatly exceeds that of wooden shores of the same length in isolated and multi-post shoring systems. A wooden shore fails by buckling under compression load. The failure of an adjustable steel tube shore in tests is due to buckling when the shore length exceeds 3.96 m, and the failure will be resulted from damage of connecting tube lock if the shore length is less than 3.96 m. When the top block of the adjustable steel tube shore is a wooden stringer, the load capacity is remarkably less than when it is a steel block. Adjustable steel tube shores will be reduced in load capacity after reuses. The load capacity of an isolated shore is reduced when the shore is placed on an inclined base. Reinforcing an isolated wooden shore with horizontal wooden bars and iron wires increases its load capacity. However, when an isolated wooden shore is reinforced with lateral cable bracings, the load capacity is not affected. Inserting the woodblock under an isolated wooden shore on an inclined plane can increase the load capacity of the shore. The multi-post shoring system that is reinforced with horizontal bracings only slightly affects the total load capacity of the system studied in this paper.

Modelling of steel lattice tower angle legs reinforced for increased load capacity

As a result of changes in design code requirements for wind loads, increased demand for electrical power, and the growing communication industry, retrofitting of existing steel lattice towers has become an important strategy in the transmission tower industry. At present there are two main reinforcing methods that are used in practice for lattice transmission towers. The first method involves adding a number of horizontal braces (diaphragms) to the mid-length of slender, inadequately braced members along the height of the tower; while the second method is focused on strengthening the capacity of the existing legs only by retrofitting them with additional members. In this paper, the most effective leg retrofitting method has been investigated through an experimental testing program using a one-panel angle leg retrofitting model and a nonlinear finite element (FEM) model. A 3D continuum element was developed to model the panels and bolted connections and the results are compared with those obtained from experiments, with good agreement. The model was then simplified using a simple locking system where a special technique was developed to simulate the bolt slip, which was found to be a critical issue from the experiments. The simplified model can then be extended to multi-panel modelling.

Influence of Side Stringer to Deck Deformation of Four-Lines High-Speed Railway Cable-Stayed Bridge with Double Cable Planes

Taking Beijiang Bridge as an example, using 3D finite element method, influence of side stringer to deck deformation of four-lines high-speed railway cable-stayed bridge with double cable planes is studied. The results show that the stiffness of the side stringer hardly influence the long wave of bridge deformation and the ratio of deflection to span, but significantly affects the short wave and transversal wave of the bridge deformation. The location of the side stringer influences the long wave slightly, but influences the short wave and transversal wave significantly. If the distance between the side stringer and the center of the main trusses changed, the long wave changes slightly, while the maximum short wave and transversal wave change a lot. The larger the distance, the less the transversal span of the deck and panel beams are, and the less the short wave and transversal wave are. The influence of the axial stiffness of horizontal K-shaped brace to the bridge deformation is small.

Three-dimensional finite element stress analysis: The technique and methodology of non-linear property simulation and soft tissue loading behavior for different partial denture designs

The purpose of this study was to develop and report upon a methodology for a non-linear capacity 3D modeling finite element analysis evaluating the loading behavior of different partial denture designs. A 3D finite element model using human CT data was constructed. An original material constant conversion program was implemented in the data simulation of non-linear tissue behavior. The finite element method material properties of residual ridge mucosa were found to have seven material constants and six conversion points of stress values. Periodontal tissues were found to have three constants, and two conversion points. Three magnetic attachment partial denture designs with different bracing elements were evaluated. Technical procedures for finite element model simulation of nonlinear tissue behavior properties evaluating the oral behavior of prosthetic device designs are reported for prosthodontic testing. The use of horizontal cross-arch bracing positively impacts upon the comparative stability of the partial denture designs tested.

Strengthening of Horizontal Bracing on Progressive Collapse Resistance of Multistory Steel Moment Frame

AbstractIn this study, the contribution of horizontal bracing to the resistance of a steel moment frame against progressive collapse was investigated using the alternate path method. Nonlinear dynamic analyses of two frame models with and without horizontal braces were carried out in various cases. The dynamic nonlinear analytical results indicated that compared with the model without braces, the displacements and rotation angles in the model with horizontal braces were much smaller because of the horizontal tie provided by the horizontal braces at the top story. It was observed that the horizontal braces could transfer the vertical loads originally carried by the removed column to the adjacent columns. Also, the layout of the horizontal braces was an effective means to enhance the resistance of the steel moment frame.

Comparative Research on Mechanical Behavior of Column-Bracing System between Fixed-Ended and Pin-Ended Column Base

In order to investigate the different mechanical behavior of column-bracing system between fixed-ended and pin-ended column base, a large number of column-bracing systems with fixed-ended and pin-ended column base were studied using the ANSYS program, in which random combination of the initial imperfections between columns and braces was well considered by the Monte Carlo method. Based on the above comparative study, probability density function of the bracing force was found through probability statistics and the design bracing force is obtained. The results show that the ultimate load-carrying capacity and the bracing forces of the mid-height horizontal braces of column-bracing systems with pin-ended column base are higher than that of column-bracing systems with fixed-ended column base, and the higher ultimate load-carrying capacity of the former more significantly increases the bracing forces of the mid-height horizontal braces; that the bracing forces of the mid-height horizontal braces in compression or in tension have also randomness because of the randomness of the initial imperfection of both columns and braces.

Design Method of Longitudinal Bracing Force Based on Monte Carlo Simulation

The bracing force of top horizontal braces supporting a row of columns under the only vertical load has been investigated in this paper. A large number of one-story longitudinal column-bracing systems were modeled and analyzed by second-order analysis using finite element method, in which the random combination of the initial imperfections between columns and braces was well considered by Monte Carlo method. According to the analysis results, three kinds of instability modes of one-story column-bracing system have been found, triple-normal probability density function of the top horizontal bracing forces is established based on probability statistics, and the design bracing forces are also obtained. A check method based on the vertical load analysis is supplied for the top horizontal bracing forces which are usually designed by the longitudinal horizontal load.

Residual stiffness assuring stability of steel structures

Through revisiting the classic problems of elastic and elastic-plastic buckling of frames, elastic-plastic stability of beam-columns, buckling of column braced at mid-span by a horizontal brace and the buckling of dual structural systems, the paper proposed the concept of 'residual stiffness', i.e., the residual part of the total stiffness after deducting the stiffness depleted by horizontal forces and bending moments in the members. Check for stability of members and structures in real steel structures is to assure a minimum residual stiffness of the members and structures to resist against the destabilising effect of gravitational loads. Through analysis of the instability of beam-columns and dual structural systems, it is revealed that in the limit state, the stiffness due to the horizontal load (bending moment) is linearly or more than linearly decreased.

The Influence of Different Scenarios of Supply Ship Collision on the Dynamic Response of a North-Sea Jacket-Pile-Soil System

In the present study, the influence of various scenarios of supply ship collisions, namely, bow, stern, and also broad-side impacts on a jacket-pile-soil system, is investigated. In the previous study of ship impact on an eight-leg North-Sea jacket platform by Amdahl and other authors, the effect of jacket-pile-soil interaction was not considered. The collision points on the jacket structure are also taken as joints and midspan of leg, horizontal and vertical braces, namely, hard and soft impact points. The speed and the weight of the colliding vessel are also varied for typical supply vessels. Several supply ship collision analyses are carried out for bow, stern and broad-side impact scenarios on an eight-leg North-Sea jacket platform. It is observed that by taking into account the jacket-pile-soil interaction effects, particularly in softer clayey soils, the amplitude of displacement response after the supply ship impact at the deck level is increased due to yield in the upper soil layers. Contrary to this finding, less linear dynamic effects can be seen in the studied jacket-pile-soil system subjected to the supply ship impact. It can also be concluded that for a soft impact scenario, the dynamic effects in the global response of the platform located in the mainly over-consolidated (OC) clayey soil may be much less than those for a hard impact scenario on the same platform. For instance, for a brace impact at its midspan, a less significant dynamic effect has been observed than for a leg impact. The duration of impact in such cases is shown to play an important role in determining the dynamic influence of the platform response. The relative energy absorption of the platform is shown to be more for broad-side loading. It is shown that the global response of the jacket platform during the collision with a supply vessel might depend largely on the scenario of the impact and, to some extent, on the pile-soil behavior. It is found that for the bow and stern impact scenarios, the energy contribution of the local member dent or buckling might be more significant than that for the broad-side loading for which the global frame energy contribution and the overall inertia effect of the platform might be a dominant factor.

Experimental and Analytical Investigation of Concrete Filled Steel Tubular Columns

In this paper, an experimental and analytical investigation of concrete-filled steel tubular (CFST) laced columns is presented. These columns consist of four concrete-filled steel tubes that are laced together. A total of 27 experimental tests were conducted to quantify the column failure mechanism at ultimate loads. The experiments were designed to obtain the load-deflection curves. These curves were subsequently used to quantify the structural behavior for each element of the hybrid column. Experimental results indicate that the compression force in the longitudinal members dominated the failure mechanism in the CFST columns. In-plane bending occurred when member segments reached the compression failure load. The forces in the lacing members (diagonal and horizontal bracing) were found to be small and remained in the elastic range through failure. The experimental study was used to validate an analytical parametric study. The analytical study showed that increasing slenderness ratios and eccentricities reduced the ultimate load capacity. Additionally, finite-element analyses of CFST columns based on four in situ structures were performed to determine the ultimate load-carrying capacity and were subsequently compared to several building codes. On the basis of the analytical results, a new methodology for calculating the ultimate load-carrying capacity is proposed. This purposed methodology is compared with five different building codes to quantify the increased accuracy.

２級造園技能士検定課題における作業工程の分析

This research analyzes the proficiency improvement of gardening skills by measuring 30 examinees’ time required to complete each practical test tasks in the Grade 2 Landscape Gardening Exam. The examinees are comprised of four college students in 2006, seven college students in 2007, seven college students in 2008 and 12 unspecialized students in the open college course. The findings of this research are threefold. 1. After four test experiences, all the examinees reach to the level to complete the test before the timeout. 2. The degree of proficiency improvement varies in the type of skills. The examinees succeed in reducing their working time beyond the standard time limit in the following six tasks; “Setting up of Posts for Bamboo Fence”, “Installation of Natural Stones”, “Installation of Stepping Stones”, “Tree Supports”, “Planting” and“Ground Leveling”. Meanwhile, the examinees' speed performances are less improved in the following five tasks; “Setting Horizontal Braces for Bamboo Fence”, “Banding Vertical Members Together for Bamboo Fence”, “Karami-musubi (traditional quick and simplified tie) for Bamboo Fence”, Curbing” and“Flat Stone Paving”. 3. More than three times of test experiences fill the technical gaps between college students and unspecialized students.

Parametric Studies on Inter-Column Brace Forces

In past studies on the design forces of inter-column braces, only the randomness of the initial imperfections of the columns was considered and the horizontal inter-column braces located at mid-height of columns were assumed to be effective only in compression. Actually, the initial imperfections of both the columns and the braces are random variables and the combination of the initial imperfections between them is also random. In this paper, the initial imperfections of the columns and the braces were randomly taken by Monte Carlo method, and a large number of the column-bracing systems with random combinations of the initial imperfections were modeled and analyzed by second-order analysis using finite element method. The binormal probability density function of bracing forces was found based on numerical calculations, parametric analyses and probability statistics. The results indicate that random combination of the initial imperfections between columns and braces leads to the randomness of horizontal inter-column brace forces in compression or in tension. The design forces of these braces have been obtained and a design formula has also been proposed. It is found that the design forces of these braces are smaller than those given in GB50017–2003, Eurocode 3 -1992 and AS4100–1998.