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Table of Contents
1. Introduction
2. The different types of culverts
3. Loading on culverts
4. What's next?
Culvert is a buried structure, similar to bridges, consisting of single or multi-span construction with a minimum length of 3m for each span. Two horizontal slabs are cast monolithically with two or more vertical side walls, with a maximum span of 6m. Culverts convey stormwater or non-perennial streams across roadways where the soil is weak. They are suitable for difficult site conditions, require minimum maintenance and have a prolonged service life.
2. The different types of culverts:
In this section, various culvert types are described, along with models created in Midas Civil.
They are the most common type of culverts since they are economical and are easier to install. Depending on the site conditions and constraints, different shapes of pipe culverts can be seen, such as circular, elliptical and pipe arch.
Advantages:
Any desired strength is achievable by proper mix-design, thickness, and reinforcement.
They are economical and easy to install.
A pipe culvert can resist high tensile and compressive stresses.
Disadvantage:
Figure 1: Pipe Culvert
Figure 2: Pipe Culvert-3D Midas Civil model and the boundary conditions assigned
Steel, stone masonry, concrete, RCC, etc., are used to construct arch culverts. Unlike box culverts, they are erected without disrupting the water flow; construction is quick. Arch type of culvert maintains the wash bed's natural integrity and is called a low-profile culvert.
Advantages:
- Greater spans can be achieved by arch action.
- Greater hydraulic efficiency.
- It can be constructed without disrupting the water flow.
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Disadvantages:
- Need stable support. The soil bearing capacity should be high enough to withstand the support reactions.
- Need timely maintenance.
Figure 3: Arch Culvert
Figure
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: Arch Culvert- 3D Midas Civil model and the displacement contour due to vertical earth pressure
Pipe-Arch culverts are suitable for large waterway openings with a more significant hydraulic advantage. Moreover, they provide low clearance and are, much more artistic. Pipe arches are particularly useful for sites with limited headroom and a hydraulic advantage at low flows.
Advantages:
Suitable for waterways with large discharge.
An increased headroom is achieved.
Greater hydraulic efficiency is achieved.
Want more information on steel corrigated culvert pipe? Feel free to contact us.
Figure 5: Pipe-Arch Culvert
Figure
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: Pipe-Arch Culvert modelled in Midas Civil
Box culvert is a monolithically cast, rigid framed structure suitable for non-perennial streams where the soil is weak. The bottom slab reduces the pressure on the ground below. Therefore, a separate foundation is not required making them economical. Even though box culverts are easy to install, a dry surface is needed for installation.
Advantages:
Suitable for non-perennial streams, where the soil bearing capacity is low.
The bottom slab reduces the soil pressure.
They are very economical.
Figure
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: Box Culvert
Figure 8: 3D and 2D models of Box Culvert in Midas Civil
Bridge culverts act as a bridge and a culvert, thus serving a dual purpose. Generally, these culverts are rectangular and built on rivers or canals. The foundation rests below ground level, and the pavement surface is on top of the culverts.
Figure 9: Bridge Culvert
Figure
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: Bridge culvert – 3D Midas Civil model and the bending moment contour due to traffic loads
3. Loads acting on culverts
Dead loads mainly constitute the self-weight of the culverts. The weight of the wearing course, the crash barrier, and other fixed loads are also considered dead loads.
A linear horizontal soil pressure acts along the vertical walls, and weep holes release the pore pressure. A uniform vertical surcharge is applied on the top slab in deep culverts.
Most of the culverts experience moving loads throughout their lifetime. Traffic loads should be applied over culverts like bridges following the various codes used worldwide. The upcoming articles will discuss the live load dispersion on culverts and the different design codes used.
The buoyant force is the upward thrust acting on culverts due to buoyancy. In many cases, the structure gets uplifted and carried away due to strong water currents. The weight of culverts should be able to withstand this uplift.
Stresses caused due to expansion and contraction of indeterminate structures like culverts due to temperature variation are known as temperature stresses. They can be classified into 2: uniform temperature - stresses caused due to uniform heating and cooling of the structure (climatic changes) and gradient temperature stresses – caused due to differential heating and cooling of members along the section.
Apart from the above-listed loads, dynamic loads are also considered in case of rail tracks loading on top.
4. What's next?
In this blog, we briefly discussed various culverts and their models created in Midas Civil. The upcoming blog will discuss the live load dispersion on box culverts following different design codes. Stay tuned.
A precast box culvert will provide:
A HIGH QUALITY PRODUCT: Fabrication of box culvert units by experienced crews in a controlled environment ensures a high quality product. Units are cast in the plant under comprehensive quality control eliminating the drawbacks imposed by weather and site conditions.
ECONOMY: Precast box culverts are cost competitive with cast in place structures.
QUICK AND EASY ON-SITE INSTALLATION: The installation of a box culvert involves preparation of the site, placement and backfilling of box culvert sections. Depending on project size, preparation of the site may be completed in a matter of hours. This preparation work may be scheduled for immediately prior to delivery of the precast culverts to the site. Placement of the culvert units is usually carried out with a crane and is a straightforward and rapid operation.
SCHEDULE: Precast fabrication of box culvert units reduces the amount of work on-site and possible impact of weather on project schedules. The culvert sections can be installed, backfilled and placed into service immediately upon delivery to the site. Box culvert units can be preordered to allow projects to proceed on-site in early spring.
REDUCED WATER CONTROL COSTS: On projects where the work site involves a water course, a precast structure eliminates the need to maintain a dry site for the entire duration of the project to prevent damage or disruption to form work, rebar, etc. reducing water control requirements and costs.
EASE OF INSPECTION: The Purchaser has the option to inspect the box culvert units at the plant prior to delivery. With cast in place structures, deficiencies such as low concrete strength represent a costly problem as the product is already in place
DURABILITY: Precast concrete products have all the durability advantages of high quality concrete, without the concern of breakdown of protective coatings, corrosion or other problems associated with other materials. Precast concrete culverts are a low maintenance solution.
FLEXIBILITY IN DESIGN CONFIGURATIONS: Because of the nature of precast concrete products, Designers can achieve a great range in configurations in culvert layouts, geometry, alignment and capacity. Special box sections can be fabricated to meet unusual conditions or design requirements. For example, radius box sections, and angular bend sections can be fabricated to accommodate changes in alignment, transition units can be fabricated where a change in culvert size is required, wyes and tees can be fabricated to allow connection of round pipe sections to the box culvert. Our Technical team is readily available to discuss possible design options, and their feasibility.
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