There are a total of 614,387 bridges in the U.S. in 2016, of which approximately 9.1% were structurally deficient. According to the American Society of Civil Engineers’ 2017 Report Card for America’s Infrastructure, America’s backlog of bridge rehabilitation needs is $123 billion [1]. Similarly, China also has a large numbers of bridges. By 2017, there were 832,500 highway bridges in China [2], most of which were simple-support bridges [3]. However, the damage type, level and characteristics of these bridges and the actual condition of bridge structural components are not clear, which results in shortage of knowledge for effective bridge management. Moreover, insufficient condition evaluation of bridges directly leads to improper maintenance measures and unnecessary or premature rehabilitation or replacement of the structures or their components.

The evaluation or rating of the existing bridges is a continual activity to ensure the safety of the bridges, providing necessary information for decisions on bridge maintenance and management. In China, quantitative data is difficult to obtain. This makes many decisions remain in a qualitative perspective, and maintenance funds can not be well utilized. At the same time, the distribution of maintenance funds can not only stay on the technical condition of bridges or components, it should be further considered for the universality of the diseases distribution, the service time of the bridges and the types of the bridges. The acquisition of typical diseases and their causes will provide important help for the rational distribution of maintenance funds.

Therefore, with the aim to provide a fundamental information for bridge evaluation, this study focuses on investigating the technical condition of simple-support bridges in a severe cold region in northeast China. Based on the routine inspection reports performed by the Research Institute of Highway, Ministry of Transport of China, the technical condition information of 637 simple-support bridges were collected and analyzed [4]. The distribution rule of bridge's technical condition was statistically analyzed. Meanwhile, the influence of service time, design load and bridge span on the technical condition was analyzed. According to the inspection condition, the typical diseases and the proportions of simply supported bridges were given in northeast China. Finally, combined with on-site inspection and engineer experience, the causes of typical diseases were analyzed. The results can be used to identify critical components for inspection and repairing, and to assist in developing rational maintenance strategies for simple-support bridges in severe cold regions.

The Chinese code (JTG H11-2004) describes the condition evaluation method for highway bridges [4]. In this method, bridge elements are rated according to three indicators, namely defect degree, influence degree on structural function by the defects, and tendency of the development or change of the defects. A score is assigned to each indicator to evaluate the condition of the bridge elements, as shown in Table 1. Note that 0 refers to a good condition or the type that is not available, while 5 refers to a dangerous condition.

According to the scores of the bridge elements, the condition score of the whole bridge (Dr) can be calculated by Eq (1).

(1)

where R_i is the condition score of bridge element i (from 0 to 5), and is the weight of element i that is defined in Table 2.

According to the calculated results of D_r, the appraisal rating of bridges can be determined, as shown in Table 3.

To better explain the above assessment methods, an example was given. The evaluation object is a two-span simple-support bridge Through field inspection, it is found that there are a lot of circumferential cracks in the pier, and the cracks are no longer developing. There are no diseases in other bridge elements. The deficit condition evaluation for pier is show in Table 4. The calculation of D_r is show in Table 5. The appraisal rating of the bridge is Level II.

Table 4. Deficit condition evaluation for pier.

The 637 simple-support highway bridges investigated include 19 reinforced concrete (RC) T-beams, 269 RC hollow-core slabs, 42 RC solid beams, 10 RC cast-in-place slabs, 49 prestressed concrete (PC) T-beams, 81 PC adjacent box beams, and 167 PC box girders. The longest span of the bridges is 50 m, and the shortest is 5.0 m. The distribution of the bridge by length is presented in Fig. (1). The age of the bridges ranges from 3 to 19 years; about 27.63% are over 15 years or older, and the ages of most bridges are either 5 (22.30%) or 7 (43.01%) years.

Table 5. Calculation of D_r.

i	Element	Weights (Wi)	Deficit Condition of the Bridge Element(Ri)	Dr.
1	Wing wall	1	0	Dr=85.6 Appraisal rating of the bridge: Level II
2	Conical slope	1	0
3	Abutment	23	0
4	Pier	24	3
5	Foundation	8	0
6	Bearing	3	0
7	Major load-bearing elements	20	0
8	Minor load-bearing elements diaphragm, wet joint)	5	0
9	Bridge deck pavement	1	0
10	Transition slab at bridge head	3	0
11	Expansion joints	3	0
12	Sidewalk	1	0
13	Guardrail	1	0
14	Highway signs	1	0
15	Drainage	1	0
16	Regulating structure	3	0
17	Others	1	0

Fig. (1). Bridge distribution by length and age.

Four types of loads were designed for these bridges. The layout of the design loads is shown in Fig. (2). The relevant quantity of bridges designed for different loads is expressed in the round brackets.

Fig. (2). Design loads and the relevant quantity of bridge.

The monthly average temperature and total precipitation in the region is presented in Fig. (3) [5]. In addition, the annual numbers of freezing-thawing cycles are 119 in this region [6].

Fig. (3). Monthly average temperature and monthly total precipitation.

Based on the condition evaluation method described above and the routine inspection reports of the 637 simple-support bridges, the appraisal ratings were determined. The 637 simple-support bridges were all in the categories of LevelIto Level III. The proportions of rating in each span group is shown in Fig. (4); Level II is a dominant rating for all the span groups. No obvious correlation between the appraisal ratings and the span lengths was observed.

Fig. (4). Appraisal ratings vs length of single span.

Fig. (5) gives the rating proportion for each design load. In general, the appraisal ratings of bridges decrease with the increase of the design load level. As mentioned earlier, only 5 bridges were designed with load C, which were all rated as LevelII. Other groups demonstrated better statistical significance. For the 12 bridges designed with load B, 8% of which were rated as LevelI, 67% were LevelII,and the remaining were Level III. For the 199 bridges designed with load A and 421 bridges designed with load D, similar distribution was observed.

Fig. (5). Appraisal ratings vs type of design loads.

The relationship between appraisal ratings and age of the bridges is shown in Fig. (6). It has been observed that the appraisal ratings of the bridges decrease with the passage of time. For bridges with a service life of 3-5 years, 7 years and more than 15 years, the proportion of rating of “poor condition” are 14%, 22% and 43%, respectively. These bridges are generally designed for 50 years or 100 years, thus, the rapid deterioration of the bridges is a great challenge to the bridge owners.

Fig. (6). Appraisal ratings vs age of the bridges.

The damage types of the bridge elements and their proportions are shown in Table 4. Pictures of some of the typical damages are shown in (Figs. 7-11).

Fig. (7). Concrete scaling and reinforcement exposing of pier.

Fig. (8). Longitudinal crack of deck pavement.

Fig. (9). Breakage of deck joint sealing strip.

Fig. (10). Concrete scaling of guardrail.

Fig. (11). Short drainage pipes fail and reinforcement corrosion of the side RC hollow-core slabs.

As shown in Table 4 and Figs. (7-11), concrete scaling and corrosion of reinforcement are the major damages of bridges in the severe cold region. The main reasons of these damages can be attributed to the following four aspects.

This paper focuses on Technical conditions of simple-support bridges in a severe cold region in northeast China. The technical condition information of 637 simple-support bridges were collected and analyzed. From the conducted analysis and comparison, the following conclusions can be drawn:

1. There is no obvious relationship between the length of bridges and the appraisal rating. The appraisal ratings of bridges decrease with the increasing of the levels of design loading and age of the bridges. For bridges aged 3-5years, 7 years, and more than 15 years, the proportion of “poor condition” rating are 14%, 22% and 43%, respectively.
2. Cracking, concrete scaling and corrosion of reinforcement are the major defects of bridges in the severe cold region. Freeze-thaw cycles and salt induced corrosion are the major causes of the damages.
3. The drainage of water is very important in reducing bridge damages in cold regions. Good drainage facilities can significantly improve bridge Technical conditions. Meanwhile, protective measures for improving the durability of bridges should be considered in the design and construction stages to mitigate hazards created in the cold weather operations.