Development and assessment of response and strength models for bolted steel connections using refined nonlinear 3D finite element analysis

The difficulty in developing bolted connection designs lies in the limitations in existing methods to characterize their strength and typically nonlinear response due to the complex interaction of the bolts and structural components. Yet it is necessary for the engineer to be able to determine the three main connection response characteristics: stiffness, strength, and ductility to account for their influence on the overall structural response behavior. The need for better connection response characterization becomes even more crucial in a performance based design approach or when designing partially-restrained moment frames. Several welded moment resisting frame connections were found to have serious failures following the 1994 Northridge earthquake leading to more interest and research on bolted connections as an alternative. In this study a refined three dimensional nonlinear finite element modeling approach to accurately simulate the response of bolted connections is presented. Sensitivity studies of modeling parameters are also performed. A nonlinear response dataset of over 400 connection cases is generated using this approach with a parametric bolted angle connection model. The use of a parametric Richard-Abbott type function and a neural network, calibrated using the response dataset, as practical tool to model the nonlinear stiffness response of bolted connections under monotonic loading is demonstrated and assessed. Failure criteria that can be practically used in conjunction with the refined three dimensional finite element models without any additional modeling requirements are developed. The stress modified critical strain (SMCS) criterion based on the void growth and coalescence mechanism initiating ductile fracture in steel is used for determining failure in the connection member. The bolt failure criterion developed is a mechanics based model using the elliptical interaction of the tensile and shear capacity envelope. The failure criteria and bolted angle response dataset is combined to assess in detail the impact of geometry and topography of the bolted angle connections on the following response characteristics: strength, initial stiffness, plastic stiffness, and absolute ductility or the displacement capacity. Finally, using the dataset of bolted angle connection response, along with their capacities and failure modes determined using the developed failure criteria, the prying strength models in the AISC LRFD Specifications, Eurocode, and a hybrid model are assessed and found to be very conservative for some cases. Based on these results a modified Eurocode and hybrid prying strength model is proposed which greatly improves the prying strength prediction. These prying models are assessed and verified using experimental data found in literature.Ph.D.Committee Chair: Haj-Ali, Rami; Committee Co-Chair: Leon, Roberto; Committee Co-Chair: White, Donald; Committee Member: DesRoches, Reginald; Committee Member: Gentry, Russel

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