Isostatic Bridges

Bridges

Isostatic bridges are the solution most commonly used for medium-sized span lengths, of up to 55 m. They are made by using double-T beams, U beams or box girders.

1.Isostatic Bridges With Double-T Beams

This kind of bridges are the solution most commonly used for the construction of precast bridges since 1950s. The deck consists of several beams of this type and a slab which is concreted in situ on top of them. Thus, span lengths between 10 and 55 m are reached in the cheapest way.

Since the first beam was manufactured in 1945, PACADAR has produced, without interruption, millions of linear metres of double-T beams used for this kind of bridges.

Currently, PACADAR manufactures double-T beams with depths from 0.45 to 2.50 m.

Product Description

Best-known basic precast product.
Providing maximum and resistant use with minimum cross-section size.

Main Characteristics

Depth ranges between 45 cm, in the smaller ones, up to 2.5 m.
Low weight.
Material optimisation.

Types Of Structures Where It Can Be Used

Applied to isostatic solutions. Allows for spans of up to 45 m.
Solutions using cantilevers exceed these values.

Main Applications

For use in both building construction and civil engineering.
Can be used for decks of any width.
Highly recommended for expansions of existing bridges.
Perfectly suited to rail bridge decks with short spans.
An ideal solution for highly oblique bridges.

Advantages

Easy to handle and quick to assemble.
A quality industrial element at a competitive price.
Adaptable to complex geometric shapes.
Low weight per element and easy to access to difficult work site locations.

Construction Details

The distance between the beams ranges between 1 and 4 m.
A single support point at each end.
Most common spans from 10.0 m to 40.0 m.
Most appropriate depth/span ratio is around 1/18 for vehicle bridges and 1/12 for rail bridges.

2.Isostatic Bridges With U-Beams

Bridges with U beams built for High Speed Railway Lines in Spain.

PACADAR manufactures U-beams with depths ranging between 0.80 m and 2.60 m.

Product Description

A technological leap in prefabricated components the 1980s.
Its current market share is more than 30%.

Main Characteristics

Closed cellular section
Depths from 0.80 to 2.60 m.
Adequate strength-weight ratio.
A combination of a box girder and a double-T beam, with a lower flange width of just 1.72 m.

Types Of Structures Where It Can Be Used

Use in isostatic and statically indeterminate set-ups.
In statically indeterminate structures, they display an optimal strength-minimum depth ratio.
Deck widths between 11.0 and 14.0 m created with double-U beams.
Greater widths can be reached by using more U-beam units, separated between 3.0 and 7.0 m between axes.
At least 2 U-beam units in the cross-section, as they are usually arranged with a single support at each end.

Main Applications

Perfect for use in high speed train bridges with standard 14.0-m width deck.
For high speed trains, it is feasible to reach 40 m through statically indeterminate set-ups.
Appropriate for bridge decks ranging between 11.50 and 13.0 m in width.
Span lengths between piers from 25 to 45 m with simply supported spans and up to 60 m with cantilevered spans.
Applicable to heavy-load slabs, with large span lengths and separations between elements.
An opportunity to create open-plan spaces.

Advantages

Strength and resistance of the closed cellular section.
Longer distances between beams.
Unbeatable resistance capacity and load-bearing element weight ratio.

Construction Details

Typical transverse arrangement with two U-beam units.
Separations of between 5.5 and 6.5 m.
Most common span length between supports is from 25 to 45 m.
A single support point at each end.

3.Isostatic Bridges With Box Girders

This type of beam, developed by PACADAR over the last 20 years makes it possible the execution of decks with a span length of up to 40 m and a width of 13 m with an isostatic set-up using only one beam.

The latest developments of this kind of solution are curved beams of up to 50-m radius.

Product Description

It is the strongest prefabricated element at present.
It came about in response to the increased capacity of means of transport and elevation offered on the market.
Makes it possible to adopt solutions comparable to on-site bridge constructions.

Main Characteristics

Closed cellular section.
Depths from 0.80 to 2.00 m.
Great torsional stiffness.
Lower flange widths of 2.10, 3.30 and 3.96 m.
Powerful elements in creating decks 12.0 m wide with a single load-bearing element.

Types Of Structures Where It Can Be Used

Use in isostatic and statically indeterminate set-ups with constant or variable depths.
Deck widths between 8.0 and 14.0 m.
Use in curved bridges with complex geometry in both the plan view and elevation view; radii from 50 to 200 m.
Used in creating continuous span sections with double supports at each end.
At least 2 U-beam units in the cross-section, as they are usually arranged with a single support at each end.

Main Applications

Span lengths of 20-45 m in isostatic set-ups. These can be increased to 60 m with a cantilever and 80 m in statically indeterminate situations.
The torsional stiffness is made use of with large overhanging slabs and in curved bridges.
The interior space can be used as utility ducts (conduits).

Advantages

Strength and resistance of the closed cellular section.
More aesthetically appealing.
In variable depth bridges, they offer advantages over centred arches or progressive cantilever structures.
In statically indeterminate structures, they allow joint work to be done in the interior.
Quick construction and assembly, as many square meters of deck can be covered with a single element.