# Low-Cost Assessment Method for Existing Adjacent Beam Bridges
## 1 Introduction
proposed a damage-identification method based on vehicle-bridge interaction analysis and the model-updating method; the existence and severity of damage in adjacent box beam bridges can be obtained by solving the minimization problem of the objective function that is constructed using the coherence function of the response spectrum (CFRS) index and frequency residual vectors [2]. [PERSON] et al. used structural vibration information collected by accelerometers and  
Figure 1: Comparison of adjacent beams with different transverse connections [2]: (**a**) China, (**b**) Japan, (**c**) the United States, (**d**) South Korea. dynamic strain gauges installed at the bottom of girders in mid-span to identify transverse mode shape of the multi-beam system to evaluate the transmission performance of grouted joints of assembled concrete multi-girder bridges [12]. [PERSON] et al. proposed a hybrid method using physical models and vision-based measurements, and demonstrated the applicability of relative displacement ratio as the damage index of hollow-core slab bridge grouted joints by establishing a simplified spring-mass system wherein the relative displacement ratio of inspected hinge joints was extracted by computer vision-based multi-point displacement measurement methods [13]. [PERSON] defined the lateral collaborative performance indicator of assembled beam bridge grouted joints as the ratio of the linear correlation coefficients of longitudinal strain of two adjacent beams; the effectiveness and accuracy of the indicator have been proved by the good agreement of strain data analysis results and actual bridge observations [14]. Based on the literature review, it can be seen that these methods have disadvantages, such as that the static load testing method will cause traffic blocking, dynamic load testing methods are susceptible to noise interference, and finite-element (FE)-model-based methods are restricted by the accuracy of the structure model. Moreover, the sensor instrumentation costs of load testing methods make them only applicable to the special inspection of specific bridges, rather than the routine inspection of the large number of small-to-medium-span bridges. The performance assessment based on visual inspection regards grouted joints of adjacent rectangular hollow-beam (ARHB) bridges as individual elements. Condition indices of grouted joints are multiplied by component weight factors and added with other weighted-element condition indices to constitute the condition index of the whole bridge. For example, according to _AASHTO (2003)_[15], the health index H of the entire bridge is calculated by the weighted average of the element health indexes, which are the ratio of the summation of the products of the corresponding coefficient and the element quantities in each condition state to the total quantity of the element. Furthermore, the element number can be found in AASHTO CORE. In China, according to _Standards for Technical Condition Evaluation of Highway Bridges (JTG/T H21-2011)_[16], grouted joints as well as diaphragms are classified as general members of superstructure with the other two parts of the superstructure being load-carrying members and bearings, while according to the _Technical standard of maintenance for city bridge (CJJ99-2017)_[17], grouted joints are classified as a part of the transverse connections and evaluated by the penetration degree of longitudinal cracks on the bridge decks. In general, the condition score of the structure can be obtained by deducting the scores represented by the detected member damages. Although shear keys are not load-bearing members, the failure of shear keys will decimate the load distribution, causing individual girders to be exposed to live loads that are greater than the designed value. Performance assessment results based on visual inspection and current specifications cannot fully reflect the important impact of grouted joints on the bearing capacity of bridges.