January 8, 2026
The construction of highway bridges in our country has entered the stage of stock maintenance. As of 2025, there are over 350000 bridges in service, of which approximately 40% have been in use for over 20 years. The lower structure, as the main load-bearing system of the bridge, includes piers, abutments, and foundation components. The lower structure material is mostly reinforced concrete material. Under the combined action of vehicle live load and bridge span dead load, a large number of diseases occur in the bridge structure during use, seriously reducing durability. According to the survey, the typical incidence of damage to lower components such as bridge piers, abutments, and foundations is as high as 62%. Therefore, it is necessary to study the mechanism and reinforcement methods of damage to the lower structure of bridges.
This article takes an operating bridge in Wuhan as an engineering example, focusing on the study of the disease characteristics of its lower structure (including piers, abutments, and foundation systems). Through a systematic regular inspection program, the morphological characteristics, spatial distribution, and development degree of various diseases are accurately identified and quantified, and a complete disease evaluation system is established based on current standards; In the process of assessing the technical condition, comprehensive use of quantitative methods is employed
Analysis and qualitative judgment methods are used to grade and evaluate the structural performance based on detection data. Finally, multi-level treatment plans including preventive maintenance, restorative reinforcement, and structural modification are proposed for different levels of disease characteristics (such as concrete cracking, steel corrosion, and other typical damages), forming a closed-loop technical path from disease diagnosis to maintenance decision-making.
Damage and mechanism of concrete bridge substructure
The causes of diseases in the lower structure of concrete bridges can be classified into two categories: endogenous and exogenous: intrinsic quality hazards caused by survey and design defects and improper construction quality control. On the other hand, there are external factors that expose the entire bridge structure to the environment. Due to environmental factors such as soil geology, temperature, wind force, and vehicle live loads, the durability of the lower structure of the bridge decreases, resulting in cracks, rough surfaces, and uneven settlement of the foundation. The main diseases caused by different structural forms are also quite different.
Bridge pier diseases
1. Gravity bridge pier diseases
(1) Sinking and shifting
The function of bridge piers is to bear the dead load of the upper structure and the live load of the vehicle, and transfer the load to the foundation. Gravity type bridge piers have a large self weight. When the bearing capacity of the foundation is insufficient, the foundation will experience uneven settlement, causing the bridge piers to sink and shift, and seriously causing the bridge piers to crack themselves.
(2) Cracking of pier body
Gravity bridge piers are mostly made of concrete, which inevitably leads to cracks. The crack forms generated by the pier body can be divided into horizontal cracks, vertical cracks, and mesh cracks. Because the bridge pier is a large volume concrete structure, in order to meet the requirements of the pier body during concrete pouring, horizontal or vertical pouring joints need to be set up. Therefore, improper construction during pouring resulted in horizontal or vertical cracks in the pier body. The development of vertical cracks is carried out from bottom to top, from the foundation to the top of the pier. The shape of the cracks is wider at the bottom and narrower at the top. Vertical cracks are caused by poor foundation or uneven settlement of the foundation. Mesh cracks are mainly caused by improper construction. During the construction process, due to the hydration heat of concrete, the temperature difference between the inside and outside, temperature changes, and concrete shrinkage and creep, temperature stress is generated inside the concrete, resulting in mesh cracks on the pier body.
(3) Damaged pier top concrete
The damage to the concrete at the top of the pier is mainly related to the bridge bearings. When the bearing size is too small and the bridge span dead load and driving live load are transmitted through the bearings, stress concentration occurs at the top of the pier, leading to the damage of the concrete at the top of the pier.
(4) Corrosion of steel bars
The bridge pier is made of reinforced concrete material, with concrete mainly bearing compressive stress and steel bars mainly bearing tensile stress. When there are microcracks in concrete, the corrosive medium in the environment enters the interior of the concrete along the cracks. For cross sea bridges, chloride ions in seawater enter the concrete protective layer of the pier body through microcracks until they reach the location of the steel bars. Afterwards, the steel bars will corrode under the action of chloride ions, and the volume expansion of the reinforced concrete will cause the concrete protective layer to rupture.
2. Disease of pillar bridge pier
Column bridge piers are composed of two parts: the cover beam and the column. The function of the cover beam is to support the upper structure of the bridge and transfer the bridge span dead load and driving live load to the column.
(1) Cover beam disease
The cracks in the cover beam mainly include vertical cracks in the negative bending moment zone of the cover beam from top to bottom, horizontal cracks crossing the cover beam along the bridge direction, and diagonal shear cracks from bottom to top. Localized compression failure, due to the small size of the support or the influence of heavy traffic, causes excessive local stress in the concrete at the support, resulting in concrete crushing. The blocking block is squeezed and cracked, and the blocking block on the cover beam is mainly set up to prevent the beam from moving laterally and detaching from the lower pier. Due to temperature or construction errors on the main beam, the reserved gap between the stopper and the beam body is insufficient, resulting in lateral deformation under the action of vehicle load, and the stopper is squeezed and cracked. Water seepage and steel corrosion, as the cover beam is usually located at the expansion joint of the upper structure, water on the bridge deck will infiltrate through the expansion joint, causing the cover beam to be in a wet state.
(2) Column diseases
The columns under the cover beam may also suffer from defects such as exposed reinforcement, concrete peeling, and steel corrosion. Generally, vertical cracks and circumferential cracks may also appear on columns. The former is mainly caused by excessive load, uneven settlement of the foundation, and excessive thickness of the reinforced concrete protective layer. For the latter, due to the distribution of pile foundations at different positions on the embankment section, the horizontal lateral displacement in the embankment is greater than that on the embankment side within the same embankment section, resulting in differences in horizontal displacement between the top surfaces of the columns. This causes torsion on the cover beam, leading to circumferential cracks on the columns.
Bridge abutment diseases
1. Bridge pier cracking
The cracking of the platform is mainly caused by poor backfill and foundation subsidence behind the platform. Due to uneven settlement of the foundation, differences in shrinkage and creep between the abutment body and the foundation concrete, and accumulation of water in the fill soil, vertical cracks appear on the abutment body. Under the repeated pressure of soil pressure behind the platform and vehicle loads, there will be significant deformation and displacement at the top of the wing tail of the side wall, resulting in excessive stress at the intersection of the front wall and the side wall, leading to cracking. The pouring of bridge piers generally belongs to the pouring of large volume concrete. After construction, the internal hydration heat is large, and the shrinkage and creep are obvious, resulting in network cracks in the abutment body.
2. Bridge abutment displacement
The inclination and uneven settlement of bridge piers are mainly caused by poor foundation under the foundation, uneven settlement of the foundation, and water erosion. However, bridge abutment slippage often occurs on soft soil foundations. When the moisture content of the soft soil increases or plastic flow occurs, the active soil pressure on the back of the abutment increases, exceeding the anti sliding capacity of the abutment and leading to slippage.
Basic diseases
1. Foundation settlement
Due to the load transmitted from the upper structure of the foundation after construction, especially the live load of vehicles, the foundation soil will be compressed, continuously drained and consolidated, leading to foundation subsidence, and even inconsistent settlement in various parts of the foundation. In severe cases, it can cause cracking of the piers and abutments. However, most bridge structures will definitely experience foundation settlement, but as long as the settlement value is within a reasonable range, no treatment is needed.
2. Basic slip tilt
Due to the frequent impact of flowing water, the foundation may experience slippage. Due to changes in the riverbed and other factors, the overlying soil on the front wall of the bridge pier has decreased, resulting in a reduction in its anti sliding force on the bridge pier. Under the action of the backfill behind the bridge pier, the foundation of the bridge pier will slip. When the backfill behind the bridge is too high or its moisture content increases, it will cause the active soil pressure on the bridge foundation in soft soil to increase, exceeding its resistance capacity, and the foundation will also slip and tilt.
3. Basic erosion
In bridge design, the foundation burial depth is controlled by selecting general and local erosion depth values that are suitable for the upper structure, in order to reduce or avoid foundation erosion by flowing water. However, due to insufficient burial depth of the foundation during construction, the continuous mining of sand and gravel in the river crossed by the bridge, or changes in the riverbed, the foundation will be directly eroded by flowing water. With long-term erosion by flowing water, the foundation under the foundation is hollowed out, leading to other bridge diseases.
4. Basic cracking
Due to the unreasonable design of the pier and abutment, the foundation is subjected to uneven stress, resulting in excessive local stress and causing cracks in the foundation. At the same time, under external loads or frost damage, the foundation may also crack due to excessive stress.
Engineering Case
1. Project Overview
A bridge in Wuhan has a total length of 69.08 meters, as shown in Figure 1, using a 4-hole 16m prestressed concrete hollow slab bridge with a total width of 57 meters. The entire bridge is arranged with dimensions of 4.5 meters (pedestrian walkway)+6 meters (non motorized vehicle lane)+36 meters (motorized vehicle lane)+6 meters (non motorized vehicle lane)+4.5 meters (pedestrian walkway). The bridge deck is continuous at the top of the pier, and D60 expansion joints are installed at the bridge abutment. The lower structure adopts column piers and abutments, with drilled pile foundations. Design load: Urban Class A, crowd load 5KN/m2.
Figure 1 Elevation of a Bridge in Wuhan
2. Investigation of diseases in the lower part of bridge structures
According to the "Technical Condition Evaluation Standards for Highway Bridges" (JTG TH21-2011), a regular inspection of the lower structure of a bridge in Wuhan was conducted. Based on the results of the regular inspection of the bridge, a disease investigation form for the lower part of the bridge was obtained, and the investigation results are shown in Table 1.
Table 1 Investigation Form for Lower Structure Damage of a Bridge in Wuhan
According to the survey form of the lower structure of the bridge in Table 1, the bridge has local defects at the column piers and abutments. The column piers are more severely damaged, with 2 cracks appearing at the cover beam. Although the crack width is ≤ 0.3mm, the crack length is relatively long. There are 3 honeycomb and pockmarks on the column piers, with a cumulative pockmarks area of 052m2, which belongs to mild honeycomb and pockmarks. There are two concrete spalling diseases at the abutment cap, with a cumulative spalling area of 0.26m2, belonging to local concrete spalling. After investigation and research, it has been found that there are some types of defects in the lower structure of the bridge, and it is necessary to conduct a technical condition assessment of the lower structure of the bridge to determine its level.
3. Technical condition assessment of bridge substructure
By conducting regular inspections of the lower structure of the bridge, the types and quantities of defects in the lower structure are determined, and a technical condition assessment of the lower structure is required. Based on the "Technical Condition Assessment Standards for Highway Bridges" (JTG TH21-2011) and the investigation results of the lower structure defects of the bridge, the piers, abutments, and foundations are scored according to the scoring criteria shown in Table 2. Table 2 Evaluation Criteria for Technical Condition of Bridge Substructure
The calculation of the lower structure of the bridge is shown in Equation 1.
(Equation 1)
In the formula: SBCI - Technical condition score of bridge substructure,
M - number of types of lower structural components,
Wi - Type i component weights.
The technical condition score of the lower structure of the bridge is calculated to be 65 points. Through regular inspections of the entire bridge, the upper structure score is determined to be 70 points and the bridge deck system score is 60 points. The technical condition grade of the entire bridge is calculated according to Equation 2.
(Equation 2)
In the formula: Dr - overall technical condition score of the bridge,
WD bridge deck system weight,
WSP - Upper Structure Weight,
WSB - Lower structure weight.
By calculation, the overall technical condition score of the bridge is 66 points, which belongs to Class 3 bridge and requires major reinforcement of the lower structure.
Reinforcement measures for the lower structure
According to the investigation of the damage to the lower structure of the bridge, it was found that the damage occurred at the bridge piers and abutments, and the types of damage included vertical cracks, honeycomb and pockmarks, and concrete spalling.
1. Bridge pier reinforcement measures
For various vertical and diagonal cracks appearing on the cover beam or pier cap, steel plates or fiber composite materials can be pasted on both sides of the tension zone, external prestressing can be applied, beam height can be increased, and bending stiffness can be improved. For cantilever or excessively long span cover beams or pier caps, reinforcement such as adding columns under the cover beams or pier caps can also be considered. For local stress cracks at the corners of unequal height cover beams, epoxy glue can be used to seal them, and block shaped steel plates can be pasted on both sides. In case of severe cracking, anchor rods should be drilled and inserted for anchoring. For horizontal cracks, vertical cracks, and mesh cracks that appear on pier columns, if the horizontal cracks are caused by excessive bending and twisting, the first step is to minimize the constant live load torque as much as possible, such as changing the support settings, releasing the pier beam consolidation into a laterally movable support, longitudinally tensioning the external prestress on the web side of the upper structure, and changing the single column pier to a two column or three column pier. The pier column itself can be reinforced by wrapping reinforced concrete hoops, sticking steel plates or fiber composite hoops in multiple layers or in the full height range, adding slant support, columns, etc.
2. Reinforcement measures for bridge piers
The cracks under the cap can be sealed by pouring high-strength cement slurry or mortar. If it is caused by the support, the support should be replaced first. If the vertical cracks in the front wall of the platform are caused by uneven lateral settlement of the foundation and the settlement has not yet terminated, the foundation should be reinforced first, and then sealed with cement slurry or mortar. Reinforcement methods such as reinforced concrete enclosure, steel hoops, or increasing the thickness of the front wall should be used. For large-scale cracking, damage, weathering, and peeling of the platform body, external reinforced concrete hoops can be used for reinforcement.
Conclusion
In summary, there are many types of diseases in the lower part of concrete bridges, and the mechanisms of their occurrence are complex. Taking a bridge in Wuhan as the research object, regular inspections of the lower structure of the bridge were conducted, and it was found that there were cracks, honeycombing, and other defects at the piers and abutments. According to the evaluation of the overall technical condition of the bridge, the score for this bridge is determined to be 66 points, which belongs to Class 3 bridges and requires reinforcement treatment for the lower structure. Based on the damage condition of the lower structure of the bridge, measures such as pasting steel plates and wrapping reinforced concrete hoops are adopted to reinforce the bridge piers and abutments.
This study reveals the typical degradation law of concrete substructures under complex loads and environmental coupling effects through actual measurement and quantitative evaluation of typical bridge diseases, and verifies the effectiveness of the disease grading method based on layered weight scoring. The proposed external prestressing reinforcement and reinforced concrete hoop technology scheme for typical diseases such as cracks in bridge piers and concrete spalling in bridge piers has been shown to improve structural durability by more than 40% through technical and economic analysis. The maturity of this research may provide key technical support for large-scale bridge health monitoring projects during China's 14th Five Year Plan period, and assist in the digital transformation and intelligent operation and maintenance of transportation infrastructure.
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Westcoast New Area, Qingdao City ,Shandong Province ,China
