• Structural Engineering and Mechanics
• /
• 제15권1호
• /
• pp.39-52
• /
• 2003

A computer program has been developed for the optimum design of prestressed concrete beams under flexure. Optimum values of prestressing force, tendon configuration, and cross-sectional dimensions are determined subject to constraints on the design variables and stresses. 28 constraints have been used including flexural stresses, cover requirement, the aspect ratios for top and bottom flanges and web part of a beam and ultimate moment. The objective function contains cost of concrete, prestressing force and formwork. Using this function, it is possible to obtain minimum cost design, minimum weight or cross-sectional area of concrete design and minimum prestressing force design. Besides the idealized I-shaped cross-section, which is widely used in literature, a general I-shaped cross-section with eight geometrical design variables are used here. Four examples, one of which is available in the literature and the others are modified form of it, have been solved for minimum cost and minimum cross-sectional area designs and the results are compared. The computer program, which employs modified grid search optimization method, can assist a designer in producing efficient designs rapidly and easily. Considerable savings in computational work are thus made possible.

• Steel and Composite Structures
• /
• 제52권1호
• /
• pp.77-87
• /
• 2024

Analytical methods for assessment of the out-of-plane buckling of unbraced top chords of truss bridges may look obsolete while comparing them to finite element analysis. However they are, usually, superior when rapid assessment is necessary. Analytical methods consider the top chord as a bar on elastic supports provided by bracing (Holt, Timoshenko). Correct assessment of the support elasticity (stiffness) is crucial. In the case of truss bridge spans of traditional structural layout (cross-beams at the truss chord nodes only), the elasticity may be set based on the analysis of the, so called, U-frame stiffness. Here the analyses consider the U-frame itself (a pair of verticals and a cross-beam) or the U-frame with adjacent diagonals or the pair of diagonals (in the absence of verticals) and the members of the bottom chord in the adjacent panels. For all the cases, the stability analysis of the chord as a bar in compression is necessary. Unfortunately, the method cannot be applied to contemporary truss bridges without verticals, that usually have independent cross-beam decks (the cross-beams attached to truss chords at their nodes and between them). This is the motivation for the analysis resulting in the method of setting the stiffness of the equivalent U-frame for the aforementioned truss bridges. Truss girders of both, gussetless and gusseted, joints are taken into account.

• 한국산학기술학회논문지
• /
• 제14권7호
• /
• pp.3495-3501
• /
• 2013

연속경간을 가지는 I형강 교량은 내부 지점 부근에 상대적으로 큰 부모멘트가 발생하게 된다. 따라서 경제적인 단면 활용을 위하여 내부지점부위의 상부 및 하부 플랜지에 플레이트를 보강한 변단면을 사용하고 있다. 본 논문에서는 기존 탄성 횡-비틀림 좌굴식에 관한 연구를 토대로 하여 비탄성 구간에 있는 일축대칭 I형 양단 스텝보의 횡-비틀림 좌굴강도 해석을 실시하였다. 유한요소해석 프로그램인 ABAQUS가 사용되었으며, 회귀분석프로그램을 활용하여 간편 설계식을 제안하였다. 양단 스텝보에 순수휨이 작용할 때를 고려하였으며, 비선형 해석을 위해 잔류응력 및 초기변형을 고려하였다. 본 연구를 통하여 개발 제안된 식은 일축대칭 스텝보의 비탄성 횡-비틀림 좌굴 강도에 널리 사용될 수 있으며 유사연구에 크게 기여할 것이다.

• 한국공간구조학회논문집
• /
• 제2권4호
• /
• pp.29-36
• /
• 2002

The responses of composite laminated beams modeled with finite element and excited by stochastic loading are studied. The cantilevered laminated beam having a 5 ply configuration is considered. The beam is 1m long, 0.1m wide, and 0.02m thick, yielding a length to thickness ratio of L/h=50. The laminated beams was assumed to be made of Born Epoxy. The four nodes at the free end of the cantilever were loaded with identical zero-mean white noise excitations. Stress and failure analysis loaded with identical zero-mean white noise excitations is carried out. Along with the obtained results, comparison and discussion are presented for the cases of symmetric-ply, antisymmetric-ply, angle-ply, and cross-ply laminated beams.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.480-485
• /
• 2004

The applications of composite materials have increased over the past few decades in a variety of structures that require high ratio of stiffness and strength to weight ratios. Recently the thick open section composite beams are used extensively as load carrying members and stiffeners of structural elements. However, most of studies on thick composite beams are limited only to closed section beams. In this study, an open cross-section thick-walled composite beam model which includes coupled stiffness, transverse shear, and warping effects is suggested and the deflections associated with the thick-walled composite beams and thin-walled composite beams are obtained and compared with the finite element analysis results.

• International Journal of Concrete Structures and Materials
• /
• 제10권2호
• /
• pp.177-188
• /
• 2016

One of the primary concerns about the design aspects is that how to deal with the shear reinforcement in the ultra-high performance fiber reinforced concrete (UHPFRC) beam. This study aims to investigate the shear behavior of UHPFRC rectangular cross sectional beams with fiber volume fraction of 1.5 % considering a spacing of shear reinforcement. Shear tests for simply supported UHPFRC beams were performed. Test results showed that the steel fibers substantially improved of the shear resistance of the UHPFRC beams. Also, shear reinforcement had a synergetic effect on enhancement of ductility. Even though the spacing of shear reinforcement exceeds the spacing limit recommended by current design codes (ACI 318-14), shear strength of UHPFRC beam was noticeably greater than current design codes. Therefore, the spacing limit of 0.75d can be allowed for UHPFRC beams.

• Structural Engineering and Mechanics
• /
• 제66권6호
• /
• pp.703-711
• /
• 2018

In this paper is studied the effect of considering the theory of Timoshenko in the vibration of AFG beams that support ground masses. As it is known, Timoshenko theory takes into account the shear deformation and the rotational inertia, provides more accurate results in the general study of beams and is mandatory in the case of high frequencies or non-slender beams. The Rayleigh-Ritz Method is employed to obtain approximated solutions of the problem. The accuracy of the procedure is verified through results available in the literature that can be represented by the model under study. The incidence of the Timoshenko theory is analyzed for different cases of beam slenderness, variation of its cross section and compositions of its constituent material, as well as different amounts and positions of the attached masses.

• Computers and Concrete
• /
• 제19권3호
• /
• pp.227-232
• /
• 2017

This paper describes an experimental study of the cyclic performance of concrete beams reinforced with CFRP prestressed concrete prisms (PCP). The failure modes, hysteretic loops, skeleton curve, ductility, energy dissipation capacity and stiffness degradation of concrete beams reinforced with CFRP prestressed concrete prisms were analyzed. The results show that The CFRP prestressed prisms reinforced concrete beams have good seismic performance. The level of effective prestress and cross section of CFRP prestressed prisms had a little influence on the bearing capacity, the ductility and energy dissipation capacity of CFRP prestressed prisms reinforced concrete beams.

• Structural Monitoring and Maintenance
• /
• 제4권3호
• /
• pp.269-299
• /
• 2017

This paper presents a Level III damage evaluation methodology, which simultaneously, identifies the location, the extent, and the severity of stiffness damage in deep beams. Deep beams are structural elements with relatively high aspect (depth-to-length) ratios whose response are no longer based on the simplified Euler-Bernoulli theory. The proposed methodology is developed on the bases of the force-displacement relations of the Timoshenko beam theory and the concept of invariant stress resultants, which states that the net internal force existing at any cross-section of the beam is not affected by the inflicted damage, provided that the external loadings in the undamaged and damaged beams are identical. Irrespective of the aspect ratios, local changes in both the flexural and the shear stiffnesses of beam-type structures may be detected using the approach presented in this paper.

• Structural Engineering and Mechanics
• /
• 제21권3호
• /
• pp.295-313
• /
• 2005

This paper evaluates the effective width of composite steel beams with precast hollowcore slabs numerically using the finite element method. A parametric study, carried out on 27 beams with different steel cross sections, hollowcore unit depths and spans, is presented. The effective width of the slab is predicted for both the elastic and plastic ranges. 8-node three-dimensional solid elements are used to model the composite beam components. The material non-linearity of all the components is taken into consideration. The non-linear load-slip characteristics of the headed shear stud connectors are included in the analysis. The moment-deflection behaviour of the composite beams, the ultimate moment capacity and the modes of failure are also presented. Finally, the ultimate moment capacity of the beams evaluated using the present FE analysis was compared with the results calculated using the rigid - plastic method.