INDUSTRY & BUSINESS

Except for floor and foundations, Portland Cement Associations new structural laboratory —**the world's largest testing machine""*—was assembled entirely from precast concrete units. Facilities it contains for testing structural ele­ments are said to be unmatched anywhere

PCA Structural Lab Unveiled A giant test machine in itself, Portland Cement Association calls the facility "completely unique"

W O R L D ' S LARGEST testing machine" is. the way Portland Cement Associa­tion describes its new and unusual structural laboratory in Skokie, 111. In­stead of housing testing machines, the laboratory is itself a giant testing ma-d i n e able to exert test forces of more tlian 10 million pounds.

Key to the lab's capabilities is its tesst floor. It's designed, using bridge design methods, to act as a strong, hol­low concrete box girder. This girder

^ i s 12 feet deep from first floor slab to basement floor slab, and both slabs are connected by webs that are 8V 2 feet hrigh. The first floor slab is pierced \my 690 holes to which loads are applied tfciid test specimens secured. Test loads ssre produced by hydraulic jacks.

PCA says the design gives the lab an almost limitless flexibility—any struc­tural element from a short girder to a frull size floor slab or roof shell can be loaded to destruction. For example, SL slab can be subjected to local loads sas high as 30,000 pounds per square £oot, while a slab as big as the entire nesting floor can be subjected to several thousand pounds per square foot over Its whole area.

According to Eivind Hognestad, manager of the structural development section and designer of the test floor, sathe unit can handle every structural •test PCA engineers can imagine a need for—plus a little*more.

Considerable work is alread> being •conducted at the lab, such as develop­ing improved connections between pre­cast structural concrete members. Full size continuous floor systems will be tested to improve design methods for various types of concrete floor slabs, such as flat plate, flat slab, two-way slab, and slab band construction, Methods of achieving continuity be­tween prestressed members are being

studied* with particular emphasis on precast, prestressed bridges. Repeated load tests of prestressed girders will be carried out.

A 66-foot prestressed concrete beam breaks under 7 1 / 2 times its desigra load; part of a program to develop better methods of achieving continuity between prestressed beams. Other aims: improve connections between precast concrete elements, improve the design of various types of concrete floor srystems

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