# Influence of Construction Joint and Bridge Geometry on Integral Abument Bridges
## 4 Bridge Response Results
### Pile Moment  
Absolute pile moments as a function of AB joint stiffness, backfill height, and bridge length under bridge contraction and expansion are presented in Figure 11g.i. All pile moments were within the plastic moment \(\varphi\)M\({}_{\text{plastic}}\) = 263 kN-m of an HP310 \(\times\) 110; however, \(\varphi\)M\({}_{\text{yielding}}\) = 172 kN-m was exceeded in some cases. In this study, elastic beam elements were used in FE models because actual bridge piles may be designed for thermal movement and most of them are intended to remain within the elastic range.  
Pile moment was significantly affected by AB joint stiffness, bridge length, and backfill height, and increased as AB joint stiffness and bridge length increased. The relationship between pile moment and backfill height was not proportional. Steel (STL) girder IABs tended to produce a larger pile moment than did PSC girder IABs. Pile moments of steel and PSC girders were significantly affected by the following factors, in order of importance: AB joint stiffness > bridge length > backfill height.  
Bridge length significantly influenced the pile moment. It is believed that the amount of abutment displacement is mostly determined by bridge length. Pile moments in 61.0, 121.9, and 182.9 m steel and PSC girder IABs varied 0.97, 1.46, and 1.93 times and 2.18, 1.42, and 2.53 times higher than those in 30.5 m long IABs.  
AB joint stiffness significantly influenced the pile moment. AB joint stiffness is important to predict the pile moment because the moment induced by bridge thermal movement is transferred to the abutment through the AB joint. As the AB joint stiffness increased, it is expected the superstructure moment is fully transferred to the pile head. Pile moments in steel girder IABs with PA standard and rigid AB joint increased 1.52 and 2.14 times higher than those with hinged AB joint. Pile moments in PSC girder IABs with PA standard and rigid AB joint increased 1.17 and 1.60 times higher than those with hinged AB joint.  
Backfill height influenced pile moments, but it was not proportional. Steel girder IABs showed larger pile moment than did PSC girder IABs. Pile moments in steel and PSC girder IABs with 4.6 and 6.1 m high backfill varied 0.74 and 0.99 times and 0.67 and 0.82 times less than those with 3.1 m high backfill. For both steel and PSC girder IABs, pile moments in 4.6 m high backfill produced the lowest pile moment. Generally, an increase of backfill height means an increase in backfill resistance against bridge expansion and abutment rotation. Thus, the increase of backfill height means an increase in pile head rotation. On the contrary, a decrease of backfill height reduces backfill resistance, and thus abutment translation increases. Hence, both an increase and decrease of backfill height increase pile moment through pile rotation and translation, respectively. Within the scope of this study, 4.6 m abutment height would be the optimum height.  
Based on the pile moment investigation, PSC girder IABs with hinged AB joint and 4.6 m high backfill would reduce the pile moment.