The project involves rebuilding of the Jamrat Bridge, a pedestrian access bridge that enables pilgrims to get close to the three pillars - each known as a jamrah - in order to stone them, a ritual that symbolises the stoning of the devil. This ritual forms part of the annual Islamic Hajj pilgrimage to nearby Mecca.

In the past, the vast number of pilgrims made overcrowding a constant problem, with many people trying to reach the same spots simultaneously.

At peak times there were more than a million people congregating around the area, leading to dangerous overcrowding even fatalities under the original system. Various solutions were tried, including the construction of a single deck bridge. Replacing this with the multi-storey bridge which is now under construction will greatly increase capacity and improve safety.

Work began in January 2006 and completion is due in October 2008. Contractor Saudi Binladen Group is casting some 450,000m³ of concrete to create the elaborate bridge structure, which is designed by Dar Consultants.

Construction is proceeding apace, with the first deck already complete and a forest of heavily-reinforced concrete columns rising steadily to support the upper levels. Doka formwork is being used to form all elements of the concrete from the column walls to the main decks.

Central to the structure’s design was the need for visitors to be able to move more easily past each jamrah. The complex ritual requires each pilgrim to throw dozens of pebbles at the pillars over the course of several days. Thanks to the new multi-storey design, they will be able to throw their stones from any of the structure's four levels, providing enormous benefits in terms of increased capacity and safer access.

A key element of the structure is the 600m-long four-storey main bridge, supported on substantial, closely-spaced in situ concrete columns. The layout is complex with some 3.5km of elevated access ramps and walkways being built as part of a one-way system designed to guide pilgrims efficiently to the focal areas from multiple entry points around the valley’s sides. Staircases, escalators and lifts provide additional routes between the levels, which also include basement and ground floor areas. The new design will ensure optimum efficiency of circulation between the various parts of the site, while filtering people towards the pillars that are central to their visit.

Each of the main decks is pierced by circular openings, to create four-storey open cylinders around the three pillars. This will funnel stones thrown from any level towards the targets – they pass through the elliptical conical floor openings to reach the basement level where collection basins are located.

The structure can have no internal columns, and the structural system consists of two series of peripheral columns at 18m standard spacing connected by an in situ edge beam. The deck floor is made of parallel box girder frames at 9m spacing and reaching 97m in span. The deck girders of the Jamarat Bridge are designed to be built with glued, match-cast, precast concrete segments using free cantilever construction technique. The prestressing of the girders is by internally bonded prestressing cables; top slab prestressing tendons are anchored in the webs at the face of each segment from one side and at the face of the back columns from the other. The bottom slab cables, which form the continuity prestressing, are anchored in bottom slab blisters.

Adjacent deck frame segments are stitched with 500mm wide sections of in situ concrete and are transversally stressed at cross diaphragm locations to form an orthotropic floor system providing a high level of redundancy and load shedding effect.

All the in situ elements are being formed using Doka systems. This includes entry and exit ramps, interchanges between levels, decks, beams, columns, lift and stairwells and several tower-mounted helipads. These have a particularly complex design, made from elegant flared concrete fins supporting the landing areas.

Creating the bridge’s wide range of structural shapes requires extensive formwork from many different Doka systems including Top 50 large area formwork, whose ease of assembly makes it ideal for the volume of work involved and the speed needed, says Doka. Two types of framed formwork are also in use. Frameco enables short framing times. It can form wall heights of up to 3m - or higher when stacked and given addition support. Frami small panel formwork is used for smaller areas as it enables fast and economical forming.

Doka 150F climbing formwork provides an economical and speedy solution for the many columns. The modular system can be quickly repositioned, keeping crane usage the minimum. It is used with Doka folding bracket K, enabling the platform and formwork to be lifted together.

“The project was particularly challenging because of the short delivery time required for such a huge quantity of formwork,” explain Doka staff Waell Bulbul and Mohammed Haneefa. “But we succeeded in meeting the demanding timescale. We produced all of the shop and assembly drawings in just one and a half months and took less than three months to deliver all the formwork needed to cast almost half a million cubic metres of concrete.”

Printer friendly version

Email this article to a friend