Bridge Inspection

1.1 Purpose of Inspection

Conduct detailed inspections, non-destructive testing, and load tests (static and dynamic) on the bridges, identifying existing defects, diseases, and their progression within the current state of the bridge structure. Evaluate the load-bearing capacity of certain bridges. Analyze the test results, determine the causes of the diseases, assess their impact on structural safety and usability, and provide reliable basis for developing maintenance plans, repair, and reinforcement design proposals for the bridges.

1.2 Testing Basis

This inspection and evaluation is conducted in accordance with the following standards, specifications, procedures, or documents:

a) Highway Bridge and Culvert Maintenance Specification (JTG H11-2004)

b) "Highway Bridge Load Test Code" (JTG/T H21-01-2015)

c) "Highway Bridge Load Capacity Testing and Evaluation Code" (JTG/T J21-2011)

d) "Highway Bridge Technical Condition Evaluation Criteria" (JTG/T H21-2011)

e) General Specifications for Highway Bridge and Culvert Design (JTG D60-2015)

f) "Highway Reinforced Concrete and Prestressed Concrete Bridge and Culvert Design Specifications" (JTG D62-2004)

g) Engineering Survey Specifications (GB 50026-2007)

h) "Code for Measurement of Building Deformation (JGJ T8-97)"

i) "Technical Code for Testing Concrete Compressive Strength by Resilometer (JGJ/T 23-2011)"

j) "Code for Inspection Technology of Reinforcing Steel in Concrete (JGJ/T 152-2008)"

k) Bridge design, construction, completion documents, and maintenance, repair, and reinforcement materials

2.1 Preliminary Preparation

The purpose of the preliminary preparation is to collect and investigate relevant information about the bridges to be inspected, providing necessary guarantees for the implementation of on-site inspections, while also specifically determining the inspection content and work priorities.

2.2 Bridge Appearance Inspection

In accordance with the provisions of the "Highway Bridge and Culvert Maintenance Code" (JTG H11-2004), conduct a detailed and individual inspection of the bridge structure's defects. Mark defects found during the inspection on-site, and make photographic records and descriptions of the disease conditions. During the inspection, use charts and textual descriptions to detail the location, extent, and severity of the defects, and evaluate their causes and trends.

2.2.1 Bridge Deck Structure Inspection

1. Is the longitudinal and transverse slope of the bridge deck comfortable, and are there any severe cracks (cracking, transverse cracks),桥头bounce, or leakage in the waterproofing layer?

2. Are there any cracks, loose parts, or leaks in the expansion joints, and are there any noticeable bounces or jumps in the vehicle?

3. Bridge deck drainage is smooth, and the drainage pipes are intact and unobstructed.

4. Are the traffic signals, signs, markings, and lighting facilities on the bridge damaged, worn out, or non-functional?

5. Are the communication, power lines, and equipment on the bridge in good condition?

2.2.2 Inspection of Upper Structure

Key inspection points for reinforced concrete and prestressed concrete beam bridges:

1. Check for damage at the end of the beam, inside the box beam for any water accumulation, and ensure good ventilation.

2. Concrete cracks, leakage, surface weathering, spalling, exposed steel reinforcement, and reinforcement corrosion.

3. Check for cracks in the concrete anchorage section of the prestressed steel strands, and whether there are longitudinal cracks along the concrete surface of the prestressed tendons.

4. At the mid-span, support points, and variable cross-sections of beam (plate) structures, check for concrete cracking, defects, and the presence of reinforcing steel corrosion.

5. Assembly bridges should be inspected for any defects in the connection areas.

6. Check for any cracks or water leakage at the junction of the composite beam's bridge deck with the beam, as well as at the joints between precast bridge decks.

7. Are the horizontal connecting components cracked? Are there any rust or fractures in the welds of the connecting steel plates? Is there any lateral movement or outward tilt in the side beams?

2.2.3 Check of the Bracket

Due to variations in the type, span, and load grade of the upper structure, the types and models of existing bridge bearings differ. When inspecting the bearings, they should be treated differently according to different situations. The main aspects include:

1. Are the bracket components intact and clean, with no cracks, misalignments, or voids?

2. How flexible is the activity support, and is the actual displacement amount normal?

3. Are there any cracks or damage on the bearing padstone?

4. Are the rubber supports aging or cracking, and do they exhibit excessive shear or compression deformation?

5. Check if the fluororubber bearing is dirty or aged.

2.2.4 Inspection of Lower Structure

The inspection of the lower structure mainly covers the following aspects:

1. Check for any sliding, tilting, settling, or uneven settlement of the pedestal and foundation.

2. Is there any settlement or bulging due to compaction of fill soil on the back of the deck?

3. Are there phenomena such as weathering, erosion, damage, and flaking in the concrete of the lower structure? Are there defects like honeycomb, rough surface, and holes?

4. Is the top surface of the pier clean? Are there any leaks at the expansion joints?

5. Inspect the concrete columns and beam caps of the bridge pier for cracks.

6. Has there been any unauthorized erosion or washout beneath the foundation, and is there any erosion around the expanded foundation base?

2.3 Non-Destructive Testing of Bridge Structures

2.3.1 Steel bar quantity, diameter, and protective layer thickness inspection

Reinforcement steel protection layer thickness measurement for concrete bridges includes the determination of steel bar location and concrete cover thickness. For bridges with missing data, an estimation of steel bar diameter should also be included. The location of steel bars and concrete cover thickness are measured non-destructively using electromagnetic methods. For bridges with missing data, verification can be conducted by localized damage methods at non-critical load-bearing parts of the structure.

In accordance with the "Code for Inspection and Evaluation of Load-bearing Capacity of Highway Bridge Structures" (JTG/T J21-2011), the thickness of the concrete beam bridge reinforcement protective layer should be inspected at the following locations:

1) Main components or load-bearing parts

2) The rebar corrosion potential test results indicate the potential areas where rebar corrosion may activate.

3) Areas where reinforcing steel has corroded and expanded.

4) Areas for setting up concrete carbonization measurement sections.

2.3.2 Concrete Carbonation Depth Detection

The degree of carbonation of concrete is one of the important indicators for evaluating the quality and durability of concrete. The condition of concrete carbonation can be detected by observing the reaction thickness of an acid-base indicator at the fresh concrete section.

2.3.3 Concrete Strength Testing

Based on the specific characteristics and requirements of various bridge sizes, structural forms, disease features, and damage conditions, select the sampling scope and number of test areas for concrete strength testing. The testing objects include major load-bearing components such as beams, main arch rings, pier bodies, cover beams, and pier columns.

The rebound method involves using a spring to drive a heavy hammer, which strikes the concrete surface through a rebound rod. The distance the hammer is反弹 back is measured, using the rebound value as a strength-related indicator to estimate the concrete strength. This method employs a rebound meter to measure rebound values in various structural concrete areas. After adjusting for testing angles and casting surfaces, the carbonization depth values detected within the rebound area are combined with strength curves established according to regulations to obtain the concrete strength value.

2.4 Bridge Deck Line Measurement

The bridge's linear condition reflects its loading state. By measuring the entire bridge's geometry, the current linear changes can be determined to provide a basis for analyzing the bridge's loading state and load-bearing capacity.

2.5 Structural Dimension Measurement

Field-measured data of bridge structural geometric shape parameters can be used to determine changes in the long-term load condition of bridge structures, as well as to infer and assess the displacement of the structural foundation.

2.6 Static Load Test

Load testing is an effective method for assessing the working condition and operational performance of bridge structures. By applying static loads to the bridge span, we can measure the stress and deflection at various control sections under test loads, thereby verifying whether the strength and rigidity of the bridge structure meet design and specification requirements. This evaluation helps assess the working condition and operational performance of the bridge structure.

Loading Scheme: The test employs a graded loading method, with each grade's load being retreated by the loading vehicle to Identify the location, carry the load until deformation stabilizes, then collect data. After unloading, continue to monitor until the structure stabilizes.

2.7 Dynamic Load Test

Dynamic Load Test, by passing various speeds within the designed operational speed through the bridge under test loads, obtaining the dynamic response of the bridge structure at different speeds, understanding the working performance of the bridge structure under live load; Vibration Test, by obtaining and analyzing the free vibration response of the bridge structure in the natural environment, understanding the dynamic characteristics of the structure. Through the analysis of dynamic response and dynamic characteristics, evaluate the dynamic performance and operational performance of the bridge structure, as well as whether it meets the usage requirements.

Test Object: Upper Structure Main Beam

Test Content:

1. The test involved a heavy vehicle driving over the bridge surface at a uniform speed of 20km/h, 25km/h, and 30km/h, respectively, with the dynamic stress (strain) and deflection at all dynamic measurement points recorded.

2. Self-vibration Frequency Test

2.8 Technical Evaluation, Analysis, and Recommendations

This bridge structure regular inspection adopts the "Technical Condition Evaluation Standard for Highway Bridges" (JTG/T H21-2011) for evaluation, covering components, parts, deck system, upper structure, lower structure, and overall bridge assessment. The technical condition evaluation combines a layered comprehensive evaluation method with five categories of bridge single-item control indicators. First, evaluate the indicators based on the technical condition evaluation tables of each detection index in the respective chapters, determining the category (1~5) of each component indicator. Then, sequentially calculate the technical conditions of components, parts, upper structure (lower structure, deck system). Finally, calculate the overall technical condition of the bridge based on the technical conditions of the upper structure, lower structure, and deck system.

This bridge inspection requires the description of defects to be conducted using professional standard terminology, detailing the location, type, nature, extent, quantity, and severity of the defects. Summarize the diseases on a per-bridge basis, compile a total summary of all inspected bridge diseases, and investigate the causes of the bridge diseases for comprehensive analysis.

2.9 Submission of Achievements

Upon completion of the bridge inspection, the client will be provided with a bridge inspection report and relevant engineering documents, including the following: inspection report, bridge structural inspection site record, bridge condition card, and bridge inspection photos.

The main contents of the inspection report include:

Bridge Overview

2. Purpose of Inspection

3. Testing Criteria

4. Inspection Items

5. Structural and Appearance Dimension Measurement

6. Full Bridge Appearance Defect Inspection

7. Static Load Test (not included in routine inspection as per standard)

8. Dynamic Load Test (Not included in routine inspections)

9. Key Technical Condition Inspection Points

10. Full-Bridge Technical Condition Assessment

11. Conclusion and Recommendations