# Influence of Construction Joint and Bridge Geometry on Integral Abument Bridges
## 4 Bridge Response Results
### Pile Head Displacement  
Pile head displacement with respect to AB joint stiffness, backfill height, and bridge length is presented in Figure 11j. This study used a positive sign convention for bridge contraction displacement toward the bridge. The pile head displacement during bridge expansion was not significant (averaged maximum expansion was \(-\)3.5 mm) owing to backfill resistance compared with those during bridge contraction, and this study focused on bridge contraction displacement. Pile head displacement was significantly influenced by the following factors, in order of importance: bridge length > AB joint stiffness > backfill height.  
Bridge length significantly influenced pile head displacement. For comparison purposes, free expansion displacement by AASHTO LRFD [25], which is a function of bridge length, was included in Figure 111. Pile head displacements in most of the parametric study cases were far less than the free expansion. Pile displacement increased as bridge length increased. As time-dependent effects in concrete increased bridge contraction, contraction displacements in PSC girder bridges were similar to those in steel girder bridges, despite a larger thermal expansion coefficient of steel. However, pile displacements in steel girder bridges were larger than those in PSC bridges during bridge expansion. Pile head displacement in 61.0, 121.9, and 182.9 m long steel and PSC girder IABs increased 1.23, 1.66, and 4.27 times larger and 2.12, 2.11, and 4.98 times larger than those in 30.5 m IABs, respectively.  
AB joint stiffness significantly influenced pile head displacement. Pile head displacement tended to increase as AB joint stiffness increased. Pile head displacement in steel girder IABs with PA standard and rigid AB joint increased 1.56 and1.83 times larger than those in IABs with hinged AB joint, respectively. Pile head displacement in PSC girder IABs with PA standard and rigid AB joint increased 1.58 and 1.48 times larger than those in IABs with hinged AB joint, respectively. When the hinged AB joint is installed, some of the superstructure thermal movement is accommodated by the rotation of AB joint. On the contrary, rigid AB joint forces the abutment to displace along the bridge longitudinal axis with less rotation, which increases pile head displacement. Hence, stiffer AB joints produced larger pile head displacements.  
Backfill height influenced pile head displacement. As backfill height increased, pile head displacements in both steel and PSC girder IABs decreased, especially the maximum envelopes clearly decreased. As the increase of backfill height caused an increase of backfill resistance against bridge expansion, but made the abutment easily to rotate to bridge contraction, the abutment with 3.1 m high backfill displaced in longitudinal translation, while the abutment with 4.6 and 6.1 m high backfill displaced in rotational direction, which caused the pile head to remain. The pile head displacement of steel and PSC girder IABs with 4.6 and 6.1 m high backfill decreased 0.73 and 0.85 times less and 0.51 and 0.63 times less than those of IABs with 3.1 m high backfill, respectively.