Report No.: CCEER-89-l
Title: A Comprehensive Study of the Loads and Pressures Exerted on Wall Forms by the Placement of Concrete
Authors: Bruce Douglas, Mehdi Saiidi, Robert Hayes, and Grove Holcomb
Date: February 1989
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557
This report presents the findings of a very detailed experimental and analytical investigation of the loads and stresses caused by the placement of concrete in a steel/wood wall form. Rates of placement ranged from 9 to 47 feet per hour; slumps of the fresh concrete varied from 2 to 7.5 inches; and the temperature of the concrete fell in the relatively narrow zone of 66 to 82 degrees Fahrenheit. Two walls having heights of 16 and 20 feet were studied. The majority of the experimental data for the study was obtained on a completely instrumented form such that all of the tie bar forces could be measured as function of time throughout the concrete placement operation. In addition, pressure cells were also used in order to be able to directly measure the pressure of the fresh concrete at selected locations on the face of the form.
The principal conclusions of the study are that the current ACI 347 committee recommendation that the hydrostatic fluid pressure of the fresh concrete be used at rates of placement greater than 10 feet per hour is unduly conservative and that the ACI 347 committee recommended wall formula for rates of placement between 7 and 10 feet per hour can be extended out to greater rates of placement up to the limiting hydrostatic fluid pressure if the following observations are taken into account. The maximum pressure computed from the formula must be regarded as an index pressure to generate a safe total load on the form. Experimental results from this study indicate that the actual local pressures on the form may exceed this index pressure by as much as 25 percent. This fact should be taken into consideration when designing the sheathing for the wallform, and possibly the sheathing support members. Additional experimental results indicate that the total load on the form defined by the above ACI index pressure exceeds the actual total load on the form by at least 10 percent. It was further observed that critical tie bar design load computed from the ACI extended wall pressure formula was sufficiently conservative in all the cases studied herein. These seemingly contradictory conclusions derive from the fact that the actual distribution of pressure on a wall form is much more variable than heretofore recognized (Abstract by authors).