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International Concrete Abstracts Portal

Showing 1-10 of 11 Abstracts search results

Document: 

SP183-10

Date: 

May 1, 1999

Author(s):

S. Alexander

Publication:

Special Publication

Volume:

183

Abstract:

A part from column-slab connections, almost all reinforced concrete connections can be analyzed and designed using plastic strut and tie models. The strut and tie model provides a simple, rational and highly transparent explanation for the flow of forces within a connection. By examining a unique substructure within a column-slab connection, Alexander and Simmonds (1) develop what amounts to a plastic strut and tie model for concentrically loaded connections between interior columns and two-way slabs with orthogonal reinforcement. On the basis for this model, a general design procedure for gravity-loaded column-slab connections has been developed. The resulting design procedure is simple and it handles column-slab connection problems that are not easily analyzed by existing code provisions. This paper outlines the design procedure and the important features of the model upon which it is based. The model is compared both to existing test results in the literature and to the ACI code design procedure. Two design examples are included.

10.14359/5869


Document: 

SP183-09

Date: 

May 1, 1999

Author(s):

A. Scanlon

Publication:

Special Publication

Volume:

183

Abstract:

Deflection control for two-way slab systems requires attention to both design and construction requirements. This paper discusses both aspects and provides a design example to illustrate how construction loads, cracking and time-dependent effects can be accounted for in slab deflection calculations.

10.14359/5539


Document: 

SP183-08

Date: 

May 1, 1999

Author(s):

D. Rogowsky

Publication:

Special Publication

Volume:

183

Abstract:

This paper deals with the selection of slab reinforcement and details from the perspective of serviceability. The focus is on extending traditional detailing rules to slabs with higher strength concrete, and to slab designs based on finite element analysis. Traditional detailing rules when used with the direct design method and equivalent frame method produce satisfactory slabs for "ordinary" applications. Slabs that fall outside the limits of applicability of the equivalent frame method are becoming more common due to the relatively ease with which one can obtain a finite element solution from elastic bending moments and forces. Detailing rules need to be gen33eralized to deal with higher strength concrete and the results of a finite element analysis, so that one can select reinforcement that provides adequate strength and serviceability. The issues addressed in this paper include: minimum reinforcement requirements; bar size, spacing and layout; bars oriented in non-principal monument directions; skew reinforcement; in-plane forces; and edge reinforcement. While there are other detailing issues, those discussed tend to have the most impact on slab performance and cost.

10.14359/5538


Document: 

SP183-07

Date: 

May 1, 1999

Author(s):

W. Gamble

Publication:

Special Publication

Volume:

183

Abstract:

The Equivalent Frame Method (EFM) of the ACI Code was developed when the predominate method of structural analysis was the Moment Distribution method. It was furthermore developed primarily for vertical loadings. While there exist special-purpose programs intended for slab analysis using the EFM, the purpose of this paper is to present a method of using the EFM approach with an ordinary plane-frame program. This can be accomplished for the vertical loading case by the use of a substitute moment of inertia, Iec, for the columns. For the lateral loading case, the beam which replaces the slab in the analysis has to have a reduced moment of inertia, with the reduction having two parts. One part is to reflect the state of cracking, with the second part being an "effective width" factor which depends on the panel shape.

10.14359/5537


Document: 

SP183-06

Date: 

May 1, 1999

Author(s):

S. Alexander

Publication:

Special Publication

Volume:

183

Abstract:

Hillerborg's strip method of design (1, 2) is a powerful and versatile technique for designing two-way reinforced concrete slabs and plates. The method is based on the lower bound theorem of plasticity, meaning that a design based on the strip method is always safe. The purpose of this paper is to provide an overview of the strip method, including design examples. The strip method is usually divided into tow parts. The simple strip method is used to design edge supported slabs. Many designers will recognize this as an application of the strong-band concept. The advanced strip method is used to design slabs with column supports or reentrant edge supports.

10.14359/5536


Document: 

SP183-05

Date: 

May 1, 1999

Author(s):

S. Simmonds

Publication:

Special Publication

Volume:

183

Abstract:

This paper review the requirements of the upper-and-lower-bound theorems of plasticity as they apply to continuous reinforced concrete slabs. The background and assumptions leading to Johansen's yield line theory (upper-bound) and Hillerborg's strip methods (lower-bond) are presented and the advantages and disadvantages of these two methods are discussed. The segment equilibrium method proposed by Wiesinger is described and presented as an alternative procedure. It is concluded that the theory of plasticity provides a practical solution for the design of continuous reinforced concrete slabs, particularly for slab systems with irregular support geometry.

10.14359/5535


Document: 

SP183-04

Date: 

May 1, 1999

Author(s):

W. Gamble

Publication:

Special Publication

Volume:

183

Abstract:

The yield line theory for the determination of the ultimate load for slab structures is a well documented method of analysis. The basics of the method, which can be implemented using either equations of equilibrium or virtual work equations, are briefly reviewed, using a rectangular panel with all edges supported. A more complex single panel is then considered, followed by a brief review of multi-panel failure mechanisms. The potential importance of in-place forces, both compression and tension, is noted. These forces, which can be thought of in arch or dome terms for compression and catenaries for tension, have led to slab failure loads much greater than can be explained on the basis of flexure alone in many test. This phase of behavior is seldom usable for normal design of civil structures, but may be very useful and helpful in trying to understand the behavior of and design structures to resist blast loadings.

10.14359/5534


Document: 

SP183-03

Date: 

May 1, 1999

Author(s):

S. Megally and A. Ghali

Publication:

Special Publication

Volume:

183

Abstract:

Design of connections of columns to flat slabs to ensure safety against punching failure is presented. The connections transfer shearing forces and moments between the columns and slabs. The objective is to cover the design procedure in most practical situations including: interior, edge and corner columns, prestressed and nonprestressed slabs, slabs with openings and slabs with shear reinforcement. The ACI 318-95 code requirements are adhered to where applicable. The designs are demonstrated numerical examples. Design of shear reinforcement in raft slabs, footings and walls subjected to concentrated horizontal forces is also discussed.

10.14359/5533


Document: 

SP183-02

Date: 

May 1, 1999

Author(s):

S. Woodson and T. Krauthammer

Publication:

Special Publication

Volume:

183

Abstract:

Traditionally, U.S. Government agencies have developed and maintained manuals for the design of structures to resist severe dynamic loads, I.e. blast effects. However, such manuals have been primarily directed toward structures of a military nature, and relatively little attention has been given to the design of civilian buildings to resist blast effects. The lack of concern for the blast resistance of buildings is no surprising in that the threat has been minimal. Although some design guidance for blast resistance has been available to the general public, the primary users have been petro-chemical industries that are aware of potential accidental explosions related to their normal operations (I.e., chemical plants). Historically, general design guidance, such as that of the American Concrete Institute's Committee 318 (ACI, 1995) (1) has served the public well. However, two recent events, the World Trade Center and the Alfred P. Murrah explosions, have heightened awareness in the United States of the potential need to consider blast effects in the design of some buildings. The discussion presented herein summarizes existing blast-resistant design approaches and addresses issues that are critical to the development of buildings with improved resistance to severe dynamic loads. Emphasis is given to the design and behavior of reinforce concrete structures.

10.14359/5532


Document: 

SP183-01

Date: 

May 1, 1999

Author(s):

S. Simmonds

Publication:

Special Publication

Volume:

183

Abstract:

The justification for using elastic frame analogies to determine design moments in two-way slab systems is discussed. A brief history of two-way reinforced concrete slab design leading to the current code procedures is presented. This history includes a description of the various elastic frame analogies that have existed in past codes, the reasons for changes and the research leading to improved frame analogies. This is followed by a critical review of the Equivalent Frame Method in the current code with suggestions for improving and simplifying provisions for elastic frame analogies in future codes.

10.14359/5531


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