Design provisions for stair slabs in the Bangladesh Building Code

This paper deals with the current state of the building code provisions for the structural design of concrete stair slabs in general and those proposed for the Bangladesh National Building Code (BNBC) in particular. The design of stairs has not received due attention in most building codes. As a result, stairs, as they occur with a variety of support conditions, are designed based on the individual designer's judgment. This results in considerable overdesign with some particular types of support arrangements, since their behavior is not readily understood. The recently proposed draft of the Bangladesh National Building Code provides categorical recommendations for the design of different types of stair slabs. Some of these provisions have for the first time been included in a building code. The background of the design provisions as proposed in the BNBC is presented. A critical review of the relevant provisions of BNBC as well as the American, British, and Indian codes of practice are also highlighted in this paper

FINITE-ELEMENT ANALYSIS OF PRESTRESSED AND REINFORCED-CONCRETE STRUCTURES

A practical and powerful technique for the discrete representation of reinforcement in finite element analysis of prestressed and reinforced concrete structures is presented. Isoparametric quadratic and cubic finite elements with movable nodes are developed utilizing a correction technique for mapping distortion. Reinforcing bars and/or prestressing tendons are modeled independently of the concrete mesh. Perfect or no bond as well as any bond-slip model can easily be represented. The procedure is successfully tested for bonded and unbonded reinforcement

ANALYSIS OF FRAMES WITH NONPRISMATIC MEMBERS

The linear elastic behavior of frames with nonprismatic members is investigated by using isoparametric plane stress finite elements. It is determined that the conventional methods of analysis for these types of structures lead to erroneous results. Comparison of the fixed end moments, stiffness, and carry-over factors of nonprismatic members available in the literature with those computed by finite element analysis reveals large discrepancies. Based on an extensive study, sources and magnitudes of errors are presented. Recommendations for proper modeling by using conventional frame analysis computer programs are made

RESISTANCE MECHANISMS IN RC BUILDING FRAMES SUBJECTED TO COLUMN FAILURE

There is a damage potential for the columns of building frames due to either unexpected causes such as vehicle impact, boiler explosion, or terrorist attack, or due to design or construction deficiencies aggravated by an earthquake, severe wind, or excessive foundation movement. This paper investigates the redistribution paths of released forces resulting from a column failure and identifies the basic structural defense mechanisms developed in a damaged building frame. Extensive analytical studies revealed that the effect of a column failure is localized to the beams connected to the vertical axis of the failed column and to the adjacent columns. Although the load-carrying capacity of the connected beams is far exceeded by the redistributed forces, the presence of even light architectural infill walls reduces the beam forces remarkably. It is observed and analytically demonstrated that a partially infilled building frame may survive a base-column failure without any damage to the other members. Further, it is shown that the redistributed internal forces can be predicted with reasonable accuracy by employing basic structural analysis

Circular plates on elastic foundations modelled with annular plates

In this paper, a new formulation is presented for the analysis of circular plates supported on elastic foundations. The formulation is based on the flexibility and stiffness methods of structural analysis. Classical thin plate theory for small deformations is applied to obtain the flexibility and stiffness coefficients. The circular plate is represented as a series of simply supported annular plates resting on support springs along their common edges. The computer implementation of the method is given, and solutions obtained for an illustrative case are discussed

Three-dimensional finite element analysis of shear wall buildings

A three-dimensional finite element computer analysis of multistorey building structures, made of pierced shear walls of open and/or closed cross-sections and flat plates, is presented. The computer program developed for this purpose provides a special and powerful mesh generation subroutine. A graphic program is also developed to prepare the data interactively by utilizing a screen graphic option. The structure model can be created. or modified very easily with the use of the present mesh generation program. The beams or columns can be added or cancelled with no difficulty at all. The plate finite element developed can represent the membrane as well as the bending behaviour of the shear wall and the floor components. The program developed is used to obtain solutions to some realistic structures to determine the bounds of the simplifying assumptions commonly made for the analysis of multistorey building structures. The program is also capable of performing analysis by using conventional simplified models of multistorey structures and of verifying the bounds set for the assumptions. (C) 1998 Elsevier Science Ltd and Civil-Comp Ltd. All rights reserved

Circular plates on elastic foundations modelled with annular plates

In this paper, a new formulation is presented for the analysis of circular plates supported on elastic foundations. The formulation is based on the flexibility and stiffness methods of structural analysis. Classical thin plate theory for small deformations is applied to obtain the flexibility and stiffness coefficients. The circular plate is represented as a series of simply supported annular plates resting on support springs along their common edges. The computer implementation of the method is given, and solutions obtained for an illustrative case are discussed. (C) 2000 Civil-Comp Ltd. and Elsevier Science Ltd. All rights reserved

ISOPARAMETRIC ELEMENTS WITH UNEQUALLY SPACED EDGE NODES

In the isoparametric finite element formulation, mapping of equally spaced nodes on the boundary of the master element to unequally spaced locations on the physical elements results in an unacceptable distortion. This type of distortion is defined as 'node mapping distortion' and a technique for its elimination is presented. Simple test cases demonstrate the utility of the new formulation