Bridge Survey

What is Meant by a Bridge?

Answer: A bridge refers to a structure built to allow a road or railway to cross over a body of water without obstructing the flow. In general terms, it is a structure constructed to span a deep body of water.

What is Meant by Bridge Topographic Survey?

A bridge topographic survey is a specialized type of survey that determines the landform, elevation, and other geographical features of the bridge and its surrounding area. The purpose of this survey is to collect necessary information for bridge construction, such as:

Land Structure: Analyzing the position and structure of the land for the bridge’s foundation.
Elevation Determination: Determining the elevation levels of the bridge and the surrounding areas.
Location Determination: Identifying the exact location of the bridge to ensure it is safe and functional.
Natural Obstacles: Identifying the location of natural obstacles such as rivers, canals, or other obstructions.
Geographical Data: Obtaining accurate information on the bridge’s location, height, and length.
Landform: Understanding the shape and structure of the land above and below the bridge.
Material and Construction Data: Information about the materials used in the construction of the bridge and the condition of the structure.
Safety Analysis: Assessing the safety and stability of the bridge.

Digital survey methods enhance the efficiency of the survey process and improve the accuracy and analytical capabilities of the data. This assists engineers in the design, construction, and maintenance of bridges.

What are the Types of Bridges?

Bridges can be categorized into two types:

Generally Constructed RCC Slab Bridge.
Generally Constructed RCC T-Beam Bridge.

What is a Breast Wall?

Answer: A breast wall is a wall constructed to support the girder or T-beam of a bridge.

What is the slab of a bridge called?

Answer: DE slab.

What is the coating applied on the bridge slab called?

Answer: Wearing coat.

What are the different parts of a bridge?

Answer: The structure of a bridge can mainly be divided into two parts:

Substructure – (a) Pier, (b) Abutment, (c) Wing wall, (d) Approach, (e) River training works, (f) Foundation, etc.
Superstructure – (a) Slab, (b) Girder, (c) Truss, (d) Deck for load-bearing, etc.

What is a pier?

Answer: A pier is a vertical pillar located between the spans of a multi-span bridge.

What is a turn wall?

Answer: A turn wall is a wall constructed parallel to the centerline of the road to hold the soil of the road.

Differences Between Culverts and Bridges:

A bridge is a structure built to allow passage over an obstacle, such as a body of water or another road or railway, without interrupting the traffic flow on the road or railway. Generally, a structure built to cross a deep-water body is called a bridge.

A culvert is a structure built over a shallow canal or stream for the purpose of allowing water drainage across a road.

Both culverts and bridges provide access over water bodies, roads, or other obstacles, but there are some fundamental differences between them:

1. Culvert:

Structure: A culvert is generally a small-sized structure built to allow water flow beneath a road or railway.
Size: It is usually small and constructed below the water level.
Use: Culverts are primarily used for small rivers, streams, or drainage of rainwater.
Length: The length of a culvert is usually very short, and it occupies little space under roads or railways.
Types: It is typically tube-shaped or pipe-like, made of concrete, metal, or plastic.

2. Bridge:

Structure: A bridge is a larger and more complex structure that allows vehicles and pedestrians to cross over roads, rivers, valleys, or railways.
Size: It is usually much larger than a culvert and is built above the water level.
Use: Bridges are generally used to cross large rivers, roads, railways, or valleys.
Length: The length of a bridge can vary from small to very large, often spanning vast areas.
Types: There are various types of bridges, such as suspension bridges, arch bridges, and truss bridges.

Key Differences:

A culvert is small, usually constructed for water flow and installed below the ground, whereas a bridge is larger and built over various types of obstacles.
Culverts primarily serve drainage or water flow, while bridges are designed for facilitating transportation.

Purpose of Bridge Construction

Introduction:
A structure is considered a bridge if the width or span of a drainage construction exceeds 5 meters and a road cross over it. Similarly, any structure built for the safe passage of railways or other vehicles can also be termed a bridge. Given that bridges are larger and more significant constructions than culverts, more careful consideration is required in selecting their location. For instance:

The bridge’s location should be such that the centerline of the bridge aligns with the centerline of the road at both ends, and as much as possible, the bridge’s centerline should be at a right angle to the flow of water in the canal or river.
The watercourse of the canal or river at the bridge location will remain straight. Bridges are constructed to facilitate the smooth and fast movement of vehicles and pedestrians over rivers, canals, valleys, railways, roads, or other obstacles. The banks at the bridge’s location should be elevated enough to prevent flooding water from overflowing during high water levels.
The road leading to the bridge should come over dry and firm ground, ensuring that if the road near the bridge is filled, the additional weight does not significantly sink the underlying soil layer.
The road approaching the bridge should avoid excessive bends or steep slopes.
The water flow speed at the bridge location should be moderate. High speeds can cause soil erosion, while low speeds can lead to sediment buildup, creating problems. Additionally, the location should avoid severe cross-currents or whirlpools.
The bridge location should be such that construction work is minimized.
When determining the bridge’s location, excessive emphasis should not be placed on the relatively narrow sections of the canal or river.

Types of Bridges:

Generally, there are two common types of bridges:

Simply supported R.C.C. slab bridge.
Simply supported R.C.C. T-beam bridge.

In the case of small spans, typically between 4 meters and 6 meters, constructing a one-way slab bridge is more cost-effective than a conventional R.C.C. slab bridge. The design of this type of bridge is also relatively simpler to construct. Compared to beam or girder bridges, the flooring of this type of bridge is thicker, and more reinforcement bars are used.

What is a Bridge Survey?

1. A bridge survey, also known as a bridge inspection or condition assessment, is a specialized survey and engineering process that focuses on evaluating the condition, safety, and structural integrity of bridges and other similar structures. These surveys are essential for ensuring the safety of transportation infrastructure and can also be used for maintenance and repair planning.

2. A bridge survey is necessary to identify a site, gather design information, and provide lines and grades for construction. A reconnaissance survey is conducted at all potential sites. A preliminary survey is performed at the best site to establish horizontal and vertical controls and gather information for the bridge design and construction plans. A local survey is conducted to position the bridge according to its design. During actual construction, the surveyor establishes any additional lines and grades needed for the construction foreman.

3. Identifying potential bridge locations and alignments for construction.

4. Conducting topographical mapping, surveying upstream and downstream for longitudinal and cross sections. The level is transferred from a given arbitrary benchmark and is shifted to the subsequent bank stations through reciprocal leveling when using a direct level transfer method or on the same bank.

5. Here is a detailed explanation of a bridge survey: Visual Inspection: A bridge survey generally begins with a visual inspection of the entire bridge structure. Surveyors and engineers carefully examine the bridge components, including its superstructure (the part that supports the road or railway), substructure (supporting piers and abutments), and foundation (the part below the ground). They look for signs of wear, damage, deterioration, cracks, and structural defects. Digital topography surveys should also be conducted to identify signs of damage, deterioration, or cracks.

6. Structural Measurements: Accurate measurements are taken to assess the dimensions and geometry of the bridge, including its span length, width, and height. These measurements are essential to determine whether the bridge complies with design specifications and safety standards through digital topography surveys.

7. Material Testing: Bridge surveyors may conduct material tests to evaluate the condition of materials used in bridge construction, such as concrete, steel, or wood. This may involve non-destructive testing methods, such as ultrasound or magnetic particle testing.

8. Load Capacity Analysis: Engineers use survey data to calculate the load-bearing capacity of the bridge and evaluate its ability to safely support traffic loads. This assessment helps determine whether weight restrictions are necessary or if rehabilitation or replacement is needed.

9. Environmental Impact: Bridge surveys can also assess the environmental impact of the bridge and its surroundings. This includes evaluating the conditions of waterways (if the bridge spans a river or body of water) and potential effects on wildlife and ecosystems. A digital topography survey can verify the height of the bridge above the water for navigable waterways.

10. Navigational Clearance: For bridges spanning navigable waterways, surveys determine vertical and horizontal clearances to ensure safe passage for boats and ships. A reconnaissance survey is conducted at all potential sites. A preliminary survey is performed at the best site to establish horizontal and vertical controls and gather information for the bridge design and construction plans. Digital surveys can determine the required height for the bridge to ensure navigability beneath it.

11. Safety Compliance: Bridge surveys evaluate the bridge’s compliance with safety regulations and codes, including load limits, rail lines, signage, and pedestrian accommodations. A bridge survey is necessary to identify a site, gather design information, and provide lines and grades for construction. Starting with RTK surveying ensures that all data is collected, minimizing the potential for errors in bridge construction.

12. Long-Term Planning: Data collected during bridge surveys is used for long-term planning and budgeting for bridge maintenance, repair, or replacement projects. It helps agencies prioritize which bridges need immediate attention and which can be scheduled for future work.

13. Emergency Response: In some cases, bridge surveys may be conducted quickly to assess immediate safety risks in response to natural disasters, accidents, or structural concerns, and to make decisions regarding emergency closures or repairs. The accuracy of measurements and the number and types of survey markers vary depending on the required degree of precision and the type of construction. For a strategic bridge, it can range from hand-level and sketch board work to precise measurements for prefabricated steel bridges.

14. Bridge surveys are typically conducted by qualified engineers and surveyors who are proficient in bridge construction and inspection techniques. The findings and recommendations from these surveys are essential for maintaining the safety and functionality of bridges and ensuring the continuous flow of transportation networks. Regular and thorough bridge surveys are a crucial component of infrastructure management.

Bridge Survey:

In the case of large and significant bridges, it is necessary to conduct a topographic or geospatial survey of the selected site and the bridge approach. The data obtained from the survey are plotted on a scale of 1:1000, and contour lines are projected at intervals of 1 to 2 meters, depending on the nature of the land. The following detailed information is recorded in the geospatial survey:

North-south alignment
Naming of the river and direction of flow
Names of nearby towns located at both ends of the bridge
Required width of the road over the bridge
Width of the existing access road to the bridge
Radius of curvature of the bridge access road
Description of the benchmark considered as the datum plane, including its height, and the land elevation on both sides, upstream and downstream, up to a distance of 150 meters.
Lowest water level and highest flood level
Catchment area, maximum flow at the bridge face, and maximum flow velocity
Results from trial pits, borings, etc.

Introduction of Digital Topographic Bridge Survey

Digital Topographic Bridge Survey is a modern technology-driven surveying method that utilizes digital tools and software to determine the geographical and topographic conditions surrounding a bridge. It provides critical information for bridge design, construction, and maintenance.

Key aspects of introducing the Digital Topographic Bridge Survey:

1. Use of Advanced Technology:
Digital Topographic Bridge Survey employs technologies such as laser scanning, drone surveys, GPS systems, and Geographic Information Systems (GIS). These technologies help in accurate and quick data collection.

2. Data Collection and Analysis:
Through this method, detailed maps of the height, low areas, slopes, and river paths around the bridge are created. The survey helps assess the terrain’s elevation and determine the suitability of the bridge’s location.

3. Drones and UAVs (Unmanned Aerial Vehicles):
Digital topographic surveys can be carried out swiftly and precisely using drones or UAVs. These are used to create digital mapping and 3D models of the surrounding environment, including rivers, canals, and valleys.

4. Laser Scanning and LiDAR Technology:
Laser scanning and LiDAR (Light Detection and Ranging) technology are used to create detailed 3D models of the area around the bridge. This method accurately measures ground surface irregularities and movements.

5. Accurate Design and Construction Planning:
This approach assists designers and engineers in creating accurate designs and construction plans for the bridge. Digital data enables easier determination of bridge stability and safety factors.

6. Performance and Safety Evaluation:
Digital Topographic Survey can be used to evaluate the bridge’s performance and safety both before and after construction. It helps identify any changes or damage to the bridge with precision.

7. Environmental Analysis:
This survey also helps in assessing the environmental impact of bridge construction and how it affects the surrounding ecosystem.

Digital Topographic Bridge Survey enhances the accuracy and efficiency of bridge architectural planning and construction processes, bringing significant improvements to overall project management.

Requirements and Preliminary Process of a Bridge Survey

Specifically, a bridge survey is necessary to identify a site, gather information for design, and provide lines and grades for construction.
Similarly, we conduct an exploratory survey at all potential locations to clarify the overall condition of the earth’s surface for bridge construction.
Additionally, for horizontal and vertical control, we carry out an initial survey at the site. In the same way, surveys are conducted to obtain data for design and construction planning.
Likewise, according to the bridge plan, we create a layout plan for the bridge, which is made possible through a location survey.
Furthermore, during actual construction, the surveyor can establish any additional lines and grades as requested by a construction foreman.
However, the accuracy of measurements and the type of survey markers used vary depending on the required degree of precision and the type of construction.

Moreover, the scope of a bridge survey can range from basic hand-level and sketch board work for a strategic survey to precise measurements for prefabricated steel bridges. These steps form the requirements and preliminary process of a bridge survey.

Bridge Survey Process

As a result, we provide bridge survey services through topographical and hydrological surveys.
Similarly, we collect all data in 3D modeling with high point density, which aids in bridge construction.
Additionally, we conduct the surveys using state-of-the-art technology and innovative techniques. Moreover, all data and measurements can provide precise and accurate information necessary for construction planning.
Furthermore, our team is capable of offering valuable input for bridge design and construction.
However, we supply data collected by modern machinery for the design and development of construction surveys.
We are highly confident and capable of providing construction survey services to meet the demands of modern and safe construction practices.

Bridge Surveying Service of SBSCLTD

Moreover, our firm has achieved remarkable success in providing bridge survey services in Bangladesh. Similarly, these services are in high demand due to their flexibility and reliability. Furthermore, we provide these services after understanding our clients’ budget requirements. Likewise, customers can obtain these services at the most affordable prices.

Additionally, we offer a wide range of services specifically for bridge projects, including planning, design, and consulting. Furthermore, our professionals adopt a reasonable approach when designing solutions after conducting thorough engineering analyses of the land.

Bridge Surveying Services

Additionally, our firm has achieved incredible success in providing bridge survey services in Bangladesh. Similarly, these services are in high demand due to their flexibility and reliability. Moreover, we provide these services after understanding the budgetary requirements of our clients. Likewise, customers can avail of these services at the most affordable prices.
Similarly, under the comprehensive range of services offered specifically for bridge projects, we provide planning, design, and consultation services. Furthermore, our professionals adopt a practical approach when designing solutions after conducting thorough engineering analysis of the land.

Setting Out Piers of a Bridge:

This is a two-fold issue: (1) accurately determining the distance of the centerline of the bridge, which involves measuring the distance from a point on one bank of the river to a point on the opposite bank along the centerline of the road or railway; and (2) establishing the center points of each pier.

For short bridges, the distance along the axis of the bridge or the centerline distance is typically measured using a standard steel tape. However, the steel tape must meet quality standards or be compared with a certified tape. In this case, the length measurement process is similar to the baseline measurement process used in triangulation at the third phase of measurement.

On the other hand, for large or long bridges, length is generally measured using the triangulation process.

Setting Out Culvert:

The best practical method for setting out a culvert involves following the centerline of the relevant road or railway and the adjacent drain, which is considered the coordinate axis. The center point of this axis is located at the center of the culvert. By determining the coordinates in this manner, the positions of the abutments and wing wall corners of the culvert can be precisely defined. The relevant engineer is provided with the tracing of the foundation plan of the culvert. This plan must include the coordinates of the abutments and wing wall corners presented in tabular form.

In this way, as illustrated in Figure 3.16, the centerlines AB and CD correspond to the road and drain, respectively, passing through the center point O of the culvert. The coordinates of point a in the figure are 1a and a1; the coordinates of point b are 1b and b1; the coordinates of point d are 1d and d1, and the coordinates of other points follow a similar pattern.

Procedure:

A peg is driven into the center point, and a theodolite is set up on it. Then, a required number of points are carefully set or established along the line AOB. For flat terrain, only a few points are needed, but for uneven terrain, a larger number of points are required. A chaining arrow or a marked stake is placed at each point. A stake is placed between each arrow or peg. A stretched thread indicates the line AB through each arrow or peg hole.
A line CD is established perpendicular to line AB, and the required number of points is marked on it, where pegs are driven in.
The threads established along the lines AB and CD are tightened, and distances are measured along line AB as 01, 02, 03, etc., and along line CD as oa, ob, oc, etc., with pegs driven at each point.
Now, two tapes are used, and their zero ends are brought together. The relevant engineer stands at the point where the two tapes meet and instructs the chainmen to stretch the tapes. The engineer’s assistant verifies the tape measurement at point 1 of the arrow on line OB and at point b of the arrow on line OD. Thus, the zero ends of the two tapes held by the engineer indicate the positions of the points, and pegs are driven at these indicated points to mark 8 points.
Following a similar process, the coordinates of all other points are determined and marked with pegs.
Using the same procedure, the positions of the abutments and wing wall corners are established and marked.
For each abutment and wing wall, the perimeter, such as abiding, is marked by pulling a string or rope along it, and a narrow trench is dug along the line (Nicking) to mark the base perimeter.
Finally, the height of each stake is determined to ensure proper excavation depth and accurate measurement of the excavation work. If the wing wall is curved, the positions of the points above the curve are determined by taking offsets along the PQ line shown in the drawing, and both offsets and distances along PQ are measured and indicated on the plan.

Setting Out Bridges:

The setting out audit for bridges follows the same process as that for culvert installation. However, only the lines AOB and COD are established at the corners of the road or railway and the center lines of the river.

Abutment Installation:

After establishing the lines AOB and COD, the corners of the abutments are accurately positioned using the previously described process with the help of a steel tape.

first method: According to Figure 3.17, there are two points located on either bank of the existing river along the centerline of roads A and B. The line AC serves as the foundation line, positioned at a precise

right angle to the bridge’s centerline AB. The foundation line AC is measured very accurately, and the angle ∠ACB is also measured correctly using the repetition process. In this case, the number of repetitions is six.

grammatically corrected version:

Among them, the telescope is set up in the normal position three times and in the inverted position three times. Subsequently, the length of AB is determined using the following formula:

AB=ACtan⁡∠ACB=ACtan⁡ØAB = AC \tan \angle ACB = AC \tan ØAB=ACtan∠ACB=ACtanØ

There is no opportunity to verify the accuracy of the work through this method. Therefore, another foundation line AE is established upstream on the same bank of the river. The length of line AB is then determined by measuring the foundation line AE and angle ∠AEB. In this case,

AB=AEtan⁡∠AEBAB = AE \tan \angle AEBAB=AEtan∠AEB

Thus, if the two calculated values of AB are not significantly different, meaning they are close to each other, the average of the two values is considered the correct value of AB.

(b) Second Method: In this method, a foundation line is established at right angles to the centerline of the bridge on both banks, and it is extended in both upstream and downstream directions. Figure 3.18 illustrates this. The distance of the bridge’s centerline or axis is determined using the triangulation process described in the first method. Then, the center points of the piers, such as 1 and 2, on the centerline of the bridge are located.

The process for determining the positions of the center points of piers 1 and 2, as shown in the figure, is outlined below:

According to Figure 3.18, for each foundation line, the distance to the center points of piers 1 and 2 on both sides of the centerline or axis of the bridge is measured and established. In this manner, the extended intersecting lines 1-1 and 2-2 from both banks create an angle of 45° with the centerline of the bridge.
The point at which the lines 1-1 meet the centerline or axis of the bridge is marked as the center point of pier 1, and it is established through sequential observation from point 1 on both banks. Similarly, the center point of pier 2 is established at the intersection of lines 2-2.

The advantage of this method is that it does not require angular measurements to find the intersection points. Instead, the points can be determined and established through observation while standing at the corresponding points on one bank to those on the opposite bank. It is an ideal method; however, it is not always feasible, as sometimes it may not be possible to establish the foundation lines at right angles to the centerline of the bridge on both banks and extend them accordingly.

(c) Third Method: In this method, two foundation lines are established on both banks (at horizontal right angles to the axis of the bridge), either upstream or downstream. In this case, it is not necessary to set the foundation lines at exact right angles to the bridge’s axis. However, they should be set at the most suitable position and ideally at right angles. The length of the foundation lines should not be less than three-fourths of the length of the bridge; ideally, it should be equal to the length of the bridge.

Thus, according to Figure 3.17, AB represents the axis of the bridge, AC and BD are the foundation lines on both banks, and P₁ and P₂ are the center points of the piers. The lengths of the two foundation lines are measured using the same triangulation process described for the third stage. The angles ∠ABC and ∠ABD are accurately measured using a transit theodolite capable of measuring up to 20″ or 10″ and sufficient sets (generally six, comprising three sets with the telescope in normal position and three sets in inverted position) are taken through the repetition process to ensure precise determination. However, in this case, the angular closure error should not exceed 5 or 6 seconds, and for extremely important tasks, it should not exceed 2 seconds.

The length of line AB is determined independently from triangles ABC and ABD. The allowable difference between the lengths determined from both triangles should be within 1 cm for a span of 200 m, and the average of the two determined lengths is considered the correct length of the bridge’s centerline or axis.

(d) Fourth Method: This is an excellent and highly accurate method typically applied in cases requiring high levels of precision.

In this method, the geodetic quadrilateral ABCD shown in Figure 3.19 is used. The eight angles of the quadrilateral ABCD can be measured with a transit theodolite that is capable of measuring up to 10″ seconds.