of the abutting cqncrete structural units that might otherwise occur due to 

 the transmission of compressive forces that may be developed by expansion, 

 applied loads, or differential movements arising from the configuration of 

 the structure or its- settlement. They are frequently used to isolate walls 

 from floors or roofs; columns from floors or cladding; pavement slabs and 

 decks from bridge abutments or piers; and in other locations where restraint 

 or transmission of secondary forces is not desired. Many designers consider 

 it good practice to place such joints where walls change direction as in L-, 

 T-, Y-, and U-shaped structures and where different cross sections develop. 

 Expansion joints in structures are often called isolation joints because 

 they are intended to isolate structural units that behave in different 

 ways . 



Expansion joints are made when the concrete is placed, by providing a 

 space between abutting structural units for the full cross section. The 

 space is formed by the use of filler strips of the required thickness or by 

 leaving a gap when precast units are positioned. Provision for continuity 

 or for restricting undesired lateral displacement may be made by incorporat- 

 ing dowels, steps, or keyways. 



(3) Construction Joints . These are joints made at the surfaces 

 created before and after interruptions in the placement of concrete or 

 through the positioning of precast units. Locations are usually predeter- 

 mined by agreement between the engineer and the contractor, so as to limit 

 the work that must be done at one time, with least impairment of the 

 finished structure though joint locations may also be necessitated by 

 unforeseen interruptions in concreting operations. Depending on the 

 structural design they may be required to function later as expansion or 

 contraction joints having the features already described, or they may be 

 required to be monolithic; i.e., the second placement must be soundly 

 bonded to the first so as to maintain complete structural integrity. 

 Construction joints may run horizontally or vertically depending on the 

 placing sequence prescribed by the design of the structure. 



(4) Combined and Special Purpose Joints . Construction joints at 

 which the concrete in the second placement is intentionally separated from 

 that in the preceding placement by a bond breaking membrane, but without 

 space to accommodate expansion of the abutting units, also function as 

 contraction joints. Similarly, constrution joints in which a filler is 

 placed, or a gap is otherwise formed by bulkheading or the positioning of 

 precast units, function as expansion joints. Conversely expansion joints 

 are often convenient for forming nonmonolithic construction joints. 

 Expansion joints automatically function as contraction joints, though the 

 converse is only true to an amount limited to the size of gap created by 

 initial shrinkage. 



Hinge joints are joints that permit hinge action (rotation) but at 

 which the separation of the abutting units is limited by tie bars or the 

 continuation of reinforcing steel across joints. This term has wide usage 

 in, but is not restricted to, pavements where longitudinal joints function 

 in this manner to overcome warping effects while resisting deflections due 

 to wheel loads or settlement of the subgrade. In structures, hinge joints 

 are often referred to as articulated joints. 



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