Reducing distortion and internal forces in truss structures by member exchanges

Internal Forces In Members

Analysis on the stiffness iteration of segmental joints in segmental linings: Method and sensitivity analysis

This paper discusses the influence of asymmetrical anchors on guyed mast behavior under wind loads. Anchor asymmetry is due to variations on anchor levels in guyed mast placed at the top of hills. Six FEM models were developed with different guy anchor asymmetries. The mast was modeled as a three dimensional structure formed by pinned members (braced and horizontal members) and continuous members (columns). Cables were modeled with catenary formulation. Non-linear analysis under extreme wind loads was performed to calculate internal force on the guyed mast components. Comparison between members force on each model was made to assess structural behavior. Relative increments in internal forces in asymmetric models in relation to symmetric models were observed in all members. Results of this investigation show that asymmetry on anchor levels of guyed mast can produce a significant increase in internal forces of masts members, hence disregard of anchors asymmetry at guyed mast design can conduce to important errors.

The secondary internal force caused by temperature in statically indeterminate bridges are usually huge, sometime is the control factor in bridge design. Since the temperature investigation of bridge construction site is difficult to predict, there deviation between design joining temperature and actual temperature and the leaded secondary internal force is inevitable. Based on this, an adaptive temperature internal force control method is proposed. This method utilizes a pre-set steel cable. When the environmental temperature changes produce negative effects to the structure, the additional force and moment of cable with the change of environment temperature will offset the effect. This method can be widely used in the temperature internal force control of statically indeterminate bridge structures, and can effectively reduce the additional internal force of undetermined bridge structures caused by temperature differences.

Introduction. Truss structures are widespread in construction due to a number of advantages, such as economy, versatility, and scalability. Accordingly, their modeling and calculation are urgent tasks in the design of building structures. Automatic solution to these problems causes an increase in design efficiency, calculation accuracy, and lower costs. The objective of the study is to examine the functionality and operation algorithm of the software module developed by the authors that generates the geometry of two-dimensional truss structures for subsequent modeling.Materials and Methods. Following the research of the widespread truss configurations, the classification of chords available in the software under consideration is given. The method of parameterizing a truss structure is provided. This method includes base geometric parameters of the structure such as dimensions, model construction rules, and additional features, as well as a comprehensive algorithm. The software is developed in JavaScript.Results. The software module has been integrated into a web application for calculating two-dimensional rod structures. To illustrate the functionality of the software, the examples of user interface are given as well as an example problem. The example includes configuration and calculation of an inclined truss structure. The results, such as support reactions and internal forces with axial force diagram, are provided.Discussion and Conclusions. Using this software module within the framework of the tool for calculating rod structures allows for the simplified process of modeling and calculating complex truss structures, design time, and resource reduction. The software module provides tools for specifying various types of structures, applying loads and assigning properties of a rod system, which makes it a useful instrument for design engineers.

This research investigated the reliability of a newly designed steel roof truss system of an industrial building to be constructed in one of the major cities in Nigeria. The probabilistic analysis technique was done with the aid of CalREL, a general-purpose structural reliability analysis software program. The longest span truss element (consisting of 73 members), is the most critical in the system, was selected and first analysed using SAP2000 Advanced 12.0.0 finite element analysis (FEA) software program in order to obtain the forces in the steel truss members; this forms part of the inputs required in CalREL. Four load variations (referred to as load ratios in the study) were tested on the selected truss. The strengths of the truss members and other properties were determined as specified in BS 5950-1: 2000. Limit state equations were derived for the calculation of the probability of failure of the individual members of the truss system. A reliability index as a measure of structural performance and related to the probability of failure was developed for all the elements of the truss. The results showed that compression members displayed a noticeable violation of the ultimate limit state requirement, while tension members showed a negligible violation. Sensitivity factors that reflect the relative importance of the individual variables in the design of roof trusses were also presented. The estimated reliability indices also revealed structural members that require immediate redesign; though they appear satisfactory in the level of deterministic design. A probabilistic approach for the reappraisal of new and existing civil structures is well supported by the findings of this investigation.

For plane truss structure, starting from the analysis of ideal truss model, the influence of tangential deformation and angular deformation on the secondary internal force of the truss is fully considered through Python program. It is obtained through analysis that: in the ideal truss model, the Pδ second-order effect causes the member to produce tangential deformation and angular deformation, resulting in secondary internal forces. Numerical analysis shows that due to the influence of secondary internal force, the axial force error of ideal truss model can reach 19.731% and the secondary shear force is almost all the members of the truss, and the secondary moment only appears at the support. The research results have important reference value for the engineering design and high-precision internal force analysis of truss structures.

Through predict activities trend of ground fissures, given to the ground surface subsidence curve on the topper side in the next 50 years. Established a tall concrete frame construction model, using SAP2000 finite element programs, take a distance of the building depart from the fissure as analytical variables, in considering the dead load, live load, horizontal seismic action and combine with foundation differential settlement working conditions, analyze the elastic displacement and internal forces of the structure. The results showed that，in the topper side area near to the fissure, affected by the avoidance distance, the displacements and internal forces of the frame structure change remarkably. The growth and redistribution of internal forces performance are the most serious in the building base floor of framework， the internal forces change in ends of both beam and column will cause a change in the direction of bending moment， but also an inflection point of the column will change with the internal forces growth and regression.

Relevance. In recent years, composite materials have become widespread in the construction of reinforced concrete structures for industrial, civil and transport structures. It is proposed to strengthen the reinforced concrete structures of hydraulic structures with prestressed basalt composite rebar. It took an experimental and theoretical substantiation of technical solutions to strengthen the reinforced concrete structures of hydraulic structures with prestressed basalt composite reinforcement. The aim of the work was to carry out a set of experimental and theoretical studies of the stress-strain state and internal forces in low-reinforced concrete structures of hydraulic structures reinforced with prestressed basalt composite rebar. Methods. Experimental studies of the stress-strain state and internal forces were carried out on the basis of low-reinforced concrete beam-type models with interblock construction joints, harden with prestressed basalt composite reinforcement in the stretched (compressed) zones of the models. Theoretical studies of the stress-strain state and internal forces were carried out on the basis of the theory of reinforced concrete and structural mechanics. Results. As a result of the research carried out on typical low-reinforced concrete structures of hydraulic structures with interblock construction joints, the main stages of the stress-strain state of hydraulic reinforced concrete structures were formulated. Based on the data of experimental and theoretical studies, taking into account the reinforcement with prestressed basalt composite rebar, as well as with prestressed clamps in the shear zone, a method was developed for calculating the strength of low-reinforced hydrotechnical reinforced concrete structures with interblock construction joints.

The internal forces in a prestressed concrete structure are of special nature due to the existence of tendons. And flaws can be found in the traditional concept of secondary moment such that common computation method of secondary moment may produce unreasonable results. This article aims at getting a better understanding of internal forces in prestressed structures and solving the relevant problems. Starting from the basic principles of internal force analysis, a new system of internal forces is put forward by which the relationship between the compression resultant on concrete cross-section and the sectional internal forces is made clear. On this basis, a definition on the concept of current secondary moment (Mcs) is proposed and its superiority pointed out. Finally, theoretical analyses are carried out on the method for calculating Mcs in the posttentioned continuous beams with unbonded and bonded prestressing tendons.

In view of the fact that the anti sliding effect analysis of the current anchor cable and anti slide pile structure is not yet complete, research on the synergy mechanism of adjacent pile‐anchor composite structures under traffic load is carried out. Firstly, a free vibration analysis for the slope dynamic model is carried out by using a three‐dimensional finite element numerical simulation method. By improving the slope boundary conditions of time‐domain analysis, the time‐domain equation of the dynamic model of traffic load acting on the top of the slope is solved accurately, and the response law of the internal force of the pile anchor composite structure is also described. The mechanism by which the pile anchor composite structure resists against the slope sliding through the internal force increment is proposed: this internal force increment is estimated to be 73.4%, while that of anchor cable is 26.6%. The composite structure presents the coordinated sharing for sliding force. The internal force of the lower row of anchor cables is 89.48 kN larger than that of the upper row, and the internal force increment is four times larger, indicating that the lower anchor cable is more effective in slope reinforcement. As the deformation at the top of the slope is greater, the prestress of the upper anchor cable should be increased to avoid the “chain failure” caused by excessive deformation. As a result, the coordination law of internal force of pile anchor is revealed, and the anti sliding sharing mechanism is clarified. A design idea of the adjacent pile‐anchor composite structure is proposed, which takes 0.2‐0.3 times the remaining sliding force as the design value of prestressed anchor cable. The idea fully considers the anti sliding effect of prestressed anchor cables and reduces the design size of anti slide pile section, providing a theoretical support for optimization design of combined anti slide structure and saving project investment.

Pretension process analysis of prestressed space grid structures

SUMMARYSignificant effort has gone toward developing accurate and efficient displacement estimation procedures for the nonlinear multi‐degree‐of‐freedom (MDOF) system. Although the dynamic nonlinear analysis is capable of providing the high computational precision through the step‐by‐step time integration method, the simplified method is still expected and imperative for seismic design practices. The work presented in this paper focuses on the implementation of using the modal superposition method to estimate displacement responses of the nonlinear MDOF system based on the force analogy method (FAM). The current research demonstrated that the equation of motion for the nonlinear MDOF system can be decoupled, but other two governing equations in the FAM about the internal force, such as the moment and force of structural members, are not decomposable. Thus, the FAM is incorporated with the modal pushover analysis (MPA) method to determine the basic parameters of each mode such that the modal superposition method can be suitable for the solution of the nonlinear MDOF system. The procedure presented here is an approximately estimation method due to the application of MPA method. However, the value and potential for the maximum displacement estimation of the nonlinear MDOF system were demonstrated through the application in a framed structure. Copyright © 2014 John Wiley & Sons, Ltd.

Elastic supporting bars exist in many structures, like transmission tower, truss, even frame, etc. Take transmission tower for example, the load-carrying capacity of diagonal members often controls the structure's bearing capacity. Previous experiments and engineering experiences indicated that possible unsafety exists in structures when designing diagonal members according to current codes. Based on the Timoshenko elastic stability theory, the study deduces the relations between adjacent web member's internal force and stability capacity of X-shape diagonal members and K-shape ones. The calculation formula for diagonal member's effective length factor of transmission tower was obtained, which can be reference in revising the codes.

A new approach named Cross-Section Method, based on membrane force transfer mechanism, for calculating internal forces of diagonal members in a single-layer reticulated shell is presented in this paper. Relevant problems in the process of calculating the internal force by Cross-Section Method are elaborated, including determination of geometric parameters of a K6 single-layer reticulated shell, establishment of equilibrium equations and analogy methods for calculating stiffness of spring supports. Stiffness matrixes of link members and the overall structure in spherical coordinates are derived based on spatial position of each member in a K6 single-layer reticulated shell. Static experiments under full-span loads and half-span loads with a 1/10 scale model of a K6 single-layer reticulated shell, adopted in a stadium located in Chiping, Shandong, were conducted. A detailed contrast of results obtained through experiments, Cross-Section Method and FEM is presented. The internal force calculated by Cross-Section Method is close to FEM results, thus verifying the membrane force transfer mechanism and applicability of Cross-Section Method in the single-layer reticulated shell. Though experimental errors are inevitable due to corrosion of some members in the model, experimental results show approximately the same tendency. Also, the results suggest that the structural behavior under half-span loads is more unfavorable compared with full-span loads.