# Nonlinear Stiffness of Semi-Fixed Dowel Joints in Semi-Integral Bridges
## 2 Introduction to the Jingpu Bridge  
The semi-fixed dowel joints used in the retrofitted Jingpu Bridge were taken as the prototype of the model tests in this study. The Jingpu Bridge is located on the Provincial Road 208 in the Suburb of Zhangzhou City, Fujian Province, China, where it is close to the Zhangzhou Railway Station with heavy traffic. The original bridge built in early 1990s has three spans of simply supported adjacent precast prestressed concrete (PC) slabs together with a continuous 10 cm thick cast-in-place link slab over piers. Each span was 16 m long, and the slab had a width of 124 cm and a depth of 80 cm. Two expansion joints were arranged between slab ends and the back wall of the abutments. The substructure consisted of a reinforced concrete column pier and abutments supported on piles. Each pier or abutment has dual columns with diameters of 1.0 m and dual-bored piles with diameters of 1.2 m as well as a capping beam 1.2 m wide and 1.2 m deep. The whole length of the bridge was 52.8 m, and the total width was 30 m [12].  
After about 20 years of service, the Jingpu Bridge's condition had degenerated seriously. According to the inspection carried out in 2010, the main problems of the bridge occurred in the superstructure, including longitudinal and transverse cracks of the slab beams and decks, steel bar corrosion and concrete carbonation of the slab beams, concrete crush in link slabs and in the vicinity of the expansion joints. After the inspection, the condition evaluation of the bridge was performed according to the Chinese standards for technical condition evaluation (JTG/T H21-2011) [17], in which the technical condition of a bridge was evaluated to a grade of 1-5, with 1 being the best and 5 representing the worst condition. The condition score of the Jingpu Bridge was only 30.8 and rated as level 4 in the evaluation, exhibiting very poor conditions of the bridge for service. Therefore, a plan for its strengthening and retrofitting plan was proposed.  
Due to the substructure of the bridge being in good technical condition, it was determined that the strengthening and retrofitting of the bridge is only focused on the superstructure. All the deteriorated simply supported PC voided slabs were replaced by new fabricated PC voided slabs, which were first erected as simple spans and then made continuous by pouring concrete between the adjacent spans, so that no link slabs over the piers were necessary to make adjacent spans continuous again. The slab beams and the abutments were connected together and the expansion joints between them were eliminated in the retrofitted structure. The superstructure was supported on piers and abutments with the semi-fixed dowel joints to form a jointless bridge with semi-integral abutments and semi-integral piers (semi-integral bridge in short). The semi-fixed dowel joint was composed of a rubber pad and a steel dowel with a rubber sleeve, which were also called a pad and dowel bearing. The square rubber pad used in this bridge has a thickness of 40 mm and a side length of 600 mm. The steel dowel had a diameter of 32 mm and a length of 1520 mm, buried in the capping beams for 1000 mm, went through the pad for 40 mm and extended into the slab beam 480 mm. Steel bars were wrapped with a rubber sleeve with an inner diameter of the 32 mm, wall thickness of 40 mm and length of 520 mm. Each slab beam in the transverse direction has two semi-fixed dowel joints with a spacing of 400 mm, as illustrated in Figure 1. The bridge elevation before and after retrofitting is shown in Figure 2. The bridge was retrofitted from July 2014 to November 2014.