Bottom Reinforcement Research Articles

Revisiting arching in deck slabs

The arching action in concrete deck slabs of girder bridges is generally recognized and is utilized by the Ontario Highway Bridge Design Code, and some other codes, to specify an empirical design method which leads to considerable savings in the amount of reinforcement. Despite this general recognition, there are some aspects of the arching action that are yet to be explored. To the knowledge of the author, all reported laboratory and field tests on deck slabs exploring its arching action under applied loads have been conducted by measuring strains in the bottom transverse reinforcement midway between the girders. Based on the results of tests on a full-scale model of a deck slab, it has been confirmed in this note that the transverse bottom reinforcement in the deck slab acts as a tie to the internal transverse arch in the slab. Because of embedment in concrete, the force in this reinforcement is the smallest midway between the girders, and not the largest as would be the case if the slab were in pure bending. Key words: arching in slabs, deck slabs, girder bridge, punching shear, steel-free deck slabs.

Bridge-Column Footings: An Improved Design Procedure

The aim of this paper is to discuss and improve on the current highway bridge-footing design procedure. Five California highway-bridge-column footings are presented here as examples, and are analyzed by using both the current Caltrans design procedure and the proposed method, considering moments induced by lateral forces and footing depth. Considerations of passive soil pressure on the side of footings are also discussed in these case studies. The current Caltrans design procedure of neglecting moments induced by lateral forces and footings depth underestimates the soil/pile bearing reactions by about 16–78% for compression, about 27–47% for tension, about 27–75% for flexure bending moment for designing bottom reinforcement, and about 26–68% flexure bending moment for designing bottom reinforcement. The larger the footing depth and/or the shorter the column, the more unconservative the current design procedure.

Reinforced Concrete Eccentric Beam-Column Connections Subjected to Earthquake-Type Loading

Test results for four reinforced concrete eccentric beam-column connections subjected to reversed cyclic loading are reported. The specimens were part of an experimental program designed to investigate the effect of torsion, induced by earthquake motions, in eccentric frame connections. The major design parameters varied in the specimens were the beam width, the beam depth, and the amounts of top and bottom longitudinal reinforcement in the beam. From the test results, it was concluded that the presence of eccentricity in the joint reduced the strength of the connection to the extent that none of the specimens were able to attain their predicted story shear strength. To account adequately for the effect of torsion, a new equation for the effective joint width to estimate the nominal joint shear strength is proposed

Condition evaluation of concrete bridges relative to reinforcement corrosion. Volume 3. Method for evaluating the condition of asphalt- covered decks : Alongi, A.J.; Clemena, G.G.; Cady, P.D. Penetradar Corp., Niagara Falls, New York (United States), PB93-142982/GAR, 96pp. (Sep. 1992)

This volume describes the development of a technique for nondestructively determining the presence of delaminations at the top and bottom reinforcement levels. The technique employs the use of short pulse, ground-penetrating radar. Extensive radio frequency modeling of the bridge deck scenario was carried out in order to establish theoretical limits of paramters and capabilites. The best discriminant for delamination at the top renforcement level is signal attenuation, and at the bottom reinforcement level, increase in the amplitude of the bottom rebar signal. Advanced radar data acquistion and signal processing equipment and software were also developed to provide a useable system at the practical level.

Beams with Small Rectangular Opening Under Torsion, Bending, and Shear

A set of generalized strength equations based on the skewbending model has been developed to predict the torsional strength and failure mode of reinforced concrete beams with or without a small transverse opening. A torsion‐bending‐shear interaction surface is generated using the proposed strength equations. Twenty‐four rectangular reinforced‐concrete beams containing a transverse opening of constant dimensions were grouped into four different series and were tested under various combinations of torsion, bending, and shear. The parameters were the ratio between top and bottom longitudinal reinforcement, the torsion‐moment ratio, and the moment‐shear ratio. Close agreement is observed between the theoretical predictions and the test results of the writers and of other investigators.

Analytical Studies of Hysteretic Behavior of R/C Joints

A series of analytical studies on the hysteretic behavior of R/C interior beam-column joints are presented. Parameters varied include the ratio of top to bottom reinforcement, the yield strength of reinforcing bars and the bond strength along the bars anchored in the joint. The studies are based on a finite element model, which accounts for the cyclic bond deterioration along anchored bars as well as the hysteretic behavior of cracked R/C sections at beam-column interfaces, thus allowing consideration of the interaction between the two end sections of the joint.

Combined Membrane and Flexural Reinforcement in Plates and Shells

A plate or shell element subjected to membrane forces Nx,Ny,Nxy and bending moments Mx,My,Mxy, is considered. Based on equilibrium considerations, equations for capacities of top and bottom reinforcements in two orthogonal directions have been derived. An iterative method is suggested for calculating the design capacities. The proposed equations are more general and rigorous than those derived for membrane reinforcement alone and those for flexure only. For the membrane alone case, the proposed equations degenerate into the previously derived equations. For the latter, it is shown that the present practice of designing flexural reinforcement may underestimate the required capacity.

Preventing Progressive Collapse of Slab Structures

The response of slab structures after initial failure is investigated in order to determine a means of preventing progressive collapse. Analytical models for predicting the post‐failure response of slabs are presented and the predictions are compared with experimental results. These analytical models along with an experimental investigation enabled the development of simple design and detailing guidelines for bottom slab reinforcement which is capable of hanging the slab from the columns after initial failures due to punching shear and flexure.

Minimum volume of curtailed reinforcement in rectangular slabs

Abstract It is well recognized that the bottom reinforcement in rectangular slabs subjected to uniformly distributed load may be curtailed near the edges. Such reinforcement arrangements are naturally more economic than those in which the bottom reinforcement is continued to the supports. Most of the minimum reinforcement solutions for rectangular slabs deal with the latter type of reinforcement arrangement. In this paper, minimum reinforcement solutions for rectangular slabs having curtailed bottom reinforcement are presented. The solution is based on the theory of optimal plastic design for piecewise constant reinforcement. Solutions are presented for slabs with all edges fixed, and with two opposite edges fixed and the other two simply supported, for different aspect ratios of the slab. The minimum moment capacity volumes of the slab are found to be about 10–25% less than those of the slabs in which bottom reinforcement is not curtailed.

Equivalent reinforcement of a spherical bottom with a radial nozzle

Equivalent reinforcement of a spherical bottom with a radial nozzle