Steel Ribs

Definition:

Steel ribs, also known as steel arches or steel sets, are structural elements used in tunneling and underground structures to provide temporary or permanent support. They are typically made of steel beams or plates and are installed to reinforce and stabilize the excavated tunnel or underground space.

Uses/benefits:

Steel ribs are used in a wide range of construction projects, including industrial, commercial, and residential buildings. They offer several benefits, including:

Tunnel support: Steel ribs are used to provide immediate support to the tunnel walls and roof during excavation. They help prevent ground collapse and maintain stability in the surrounding soil or rock mass.
Ground control: Steel ribs contribute to ground control by distributing the loads from the surrounding rock or soil to provide structural support. This helps prevent deformation, subsidence, and potential collapses in tunneling and underground construction.
Structural integrity: Steel ribs enhance the structural integrity of the tunnel or underground space, improving its load-bearing capacity and resistance to external forces such as water pressure, seismic activity, and ground movement.
Safety: By providing structural support and stability, steel ribs ensure the safety of workers and equipment inside the tunnel or underground structures.
Temporary or permanent support: Steel ribs can serve as temporary support during construction activities, allowing the installation of other permanent support systems such as shotcrete or lining. They can also be used as permanent support elements in situations where they are designed to provide long-term structural reinforcement.

Specifications:

Steel ribs come in various sizes, shapes, and specifications, depending on the construction project requirements. The most common specifications are:

Material: Steel ribs are typically made of high-strength steel, such as structural steel or alloy steel, to provide the necessary strength and durability.
Shape and dimensions: Steel ribs come in various shapes and sizes, including I-beams, U-channels, circular arches, or custom-designed profiles. The dimensions of the ribs depend on the specific project requirements, including the tunnel diameter, roof span, and load-bearing capacity.
Connection system: Steel ribs are connected together using bolts, welding, or other fastening methods to create a continuous support structure.
Corrosion protection: Depending on the project conditions, steel ribs may require corrosion protection measures, such as coatings, galvanization, or use of corrosion-resistant steel, to prevent degradation over time.

Types:

There are several types of steel ribs, including:

Rigid steel ribs: These are solid steel beams or plates that provide substantial structural support and stiffness to the tunnel or underground structure.
Articulated steel ribs: These are segmented or hinged steel elements that allow for movement and flexibility, accommodating ground deformations or settlement.
Yielding steel ribs: These ribs are designed to yield or deform under extreme loading conditions, absorbing energy and preventing catastrophic failure.
Continuous ribs: These are used for fast erection process and favorable to rocks whose bridge action period is long enough to permit removal of gases and mucking.
Rib and Post: Generally used for the tunnels whose roof joins the side wall at an angle instead of a smooth curve. It may also used in large tunnels like Two - Lane highway tunnels.
Rib and Wall Plate: This is recommended for the tunnels having large cross section with high straight sides through good rock. The case of spalling rock, occur in the roof has also used this type of steel ribs pattern.
Full Circle Rib: Ground problems like squeezing, swelling or any rock which imposed considerable side pressure, this type of ribs has advantageous to use.

General requirements

Calculation for the spacing of ribs is given in IS 15026: 2002
Rib, wall plate, and post are suitable methods for the heading and benching methods.
Because severe roof conditions make it necessary to drive top heading first, support rib and wall type are usually suggested in the heading while post may or may not be employed in benching (depending on condition)..
The employment of the rib, wall plate, and post is helpful when using the side drift method for a large-scale tunnel under poor rock mass circumstances.

The selection of steel ribs is based on factors such as ground conditions, loadings, and anticipated deformations or movements in the tunnel or underground space.