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Sayı: 24 - Ağustos 2010


Hasan ÇALIŞLAR, Architect: “By these regulations no dainty steel builds are possible”

The biggest problem for steel today as we architects use steel in construction, we prefer showing all the structure, many of us do, however, this presents also the heat bridge issues. For architects who prefer steel the main considerations are these difficult details.

The biggest problem for steel today as we architects use steel in construction, we prefer showing all the structure, many of us do, however, this presents also the heat bridge issues. For architects who prefer steel the main considerations are these difficult details. But it is also a project management issue. Task allocation must be defined perfectly. If the structure is to be bare then there is extra load compared to reinforced concrete. On the other hand there is the fire protection; if you want to show off the steel structure then comes the expensive job of using protective paint and this has to be solved by the paint manufacturers for the steel industry. When casing is not employed as a measure, this is the case. Fire consultants can sometimes be rather paranoid about this issue. Our fire regulations on steel is very problematic. In Turkey the statics guides and the fire guides also are quite paranoiacally prepared. We have to reconsider each one separately.

DDB Salt Depot
Design Team: İ. Kerem Erginoğlu, Hasan Çalışlar, Fatih Kariptaş, Emre Erenler, Elmon Pekmez, Türkan Yılmaz
Employer: DDB
Construction Date: 2008
Covered Area: 3000 m
Construction type: Steel
With four seperate galleries over 10 meters and thick stone walls Tuzambarı is a fortified space and here mezzanie floors are designed as needed, and working volumes are connected thus. Agency’s various departments and service areas are divided into sections accordingly with these galleries. Regarding the existing empty-full relationships stone walls are saved and a second separate structure is designed with steel and glass.
In order to keep the original structure of the building all the stone wall joints were washed and then they have been enforced by solutions made as a result of chemical analysis. Any stones damaged or displaced have been restored. All the eloctro-mechanical installations were taken openly through the enforced roof girders.
The mechanical hardware was taken to the narrow yard in the back of the building over the roof by one of the largest cranes in Turkey. Spaces that have been put into steel frames can be clearly seen from the sectional view of the building. The steel roof that have been constructed by Tekel and the newly added steel frames are accentuated by being painted in different colors. The overall result appropriate for a creative work space, giving individual working areas for its personnel is a modern architectural solution with a conservationist approach.

Yapı Merkezi Cons. and Ind. Inc.
Ersin ARIOşLU, MSc, CE, Dr.h.c.
Project Owner: Khartoum State Ministry of Physical Planning and Public Utilities (MPPPU) – SUDAN
General Contractor: Yapı Merkezi Cons. and Ind. Inc.
Steel Fabrication Plant: Karçel Steel Fabrication Ind. and Trd. Inc.
Design Code: EUROCODE
Construction Period: 02.04.2008 ~ 28.02.2010
Structural Steel: 4,2x103t (165kg/m2, 235 kg/m2)

The width of River Nile reaches 900m at Al Halfaia Bridge region, (see Figure 1). The navigation channel for the ship traffic is located at the eastern end of the bridge because of the river island at the middle of the river, (see Figure 2).
The structural system of the Al Halfaia Bridge consists of two structural types. Three semi-integral composite steel bridges (Bridges 1, 2 and 3) were arranged between the Axes 1~23 and a continuous composite steel bridge (Bridge 4) of three spans at the navigation channel was utilized between the Axes 23~26 (see Figure 2). Four consecutive partial bridges with lengths of: 238.6 +284.8 + 239.2 + 147.4 m were used to span the Nile in the Al Halfaia Bridge Project.
2.1. Bridge 1, 2 and 3 (Semi Integral Bridges Axes “1~23”)
The superstructure consists of two identical double deck (see Figure 3), Deck A and B, each with a width of 13.50m (total width 27m).
The structural system between Axes 1~23 continuous composite beam along 7 spans (25m + 6x35.6m) for Bridge 1 and Bridge 3, and 8 spans (8x35.6m) for Bridge 2. The superstructure is integrated with the inner piers rigidly and forms an integral structural system.
The semi-integral structure permits a free movement and rotation of the superstructure only at the abutments or over the transition piers. According to this approach the expansion joints and bearings are placed only at the ends of each particular bridge, (see Table 1, Table 2).
The superstructure consists of 6 numbers of 140 cm steel – I – girders with a 60cm width of bottom flange, 40cm width of top flange with S355J2G3 steel quality and a reinforced concrete deck slab with a total thickness of 29 cm. The distance between the steel girders was chosen according to the use of trapezoidal steel sheets (h=70mm) with S350GD steel quality as formwork elements for the deck slab, and fixed at 2.24 m distance, (see Figure4).
The connection between the steel girders and the concrete capping beams of the piers (rigid connection) are realized by a head plate. The bending moments at supports of composite beams will convert into coupling forces by this connection and transfer the loads to reinforced concrete capping beam, (see Figure 5, Figure 6).

Regular Piers at Axes “2~7”, “9~15” and “17~22”
The regular piers underneath each deck consist of a cantilevered capping beam, an elegant column and a pile cap with a concrete quality of C30/37. The pile caps are designed above the water level of the low water period with a thickness of 1.5m. Each pile cap consist of four bored piles (L=~20m), socketed 8 meters to the sandstone with a diameter of Ø1.20m which are used as the foundation, (see Figure7).
2.2. Bridge 4 (Continuous composite steel girder, Axes “23~26”)
For the structural system of the 147.4m long Bridge 4, it is preferred to use a continuous steel composite beam system with a 64 m main span of 3 spans (42m+64m+41.4m) between Axes 23~26, (see Figure 2).
The cross section consists of two box girders with a 150cm width, and 180cm height mounted at a distance of 9.80 m and a reinforced concrete deck slab with C30/37 concrete quality and, with a total thickness of 29 cm, (see Figure 9).
The main box girders form haunches over the main piers at Axes 24 and 25 with a length of 12.00 m and the steel girder height increases from 1.80m to 3.60m, (see Figure 10).
Main Piers (Axes “24” and “25”)
Main piers are located under each deck at main Axes 24 and 25 designed visually similar to the piers of the Bridges 1, 2 and 3. The 2.0m thick pile cap is resting on 19.5m long 12 numbers of bored piles with a diameter of Ø1.50 m and C25/30 concrete quality, (see Figure 10).
2.3. Fabrication and Erection of the Steel Girders
The whole steel elements were manufactured in steel mill Karçel A.ş. in Turkey. The elements were shipped to Port Sudan. Then they were carried on trucks to Khartoum (approximately 1000 kilometers away). Due to the long transportation, the steel parts are limited to 12m length. The installations of steel beams were carried out using a mobile crane which was placed on a barge over the Nile, (see Figure 13, Figure 15).

Al Halfaia Bridge is a blend of form and function, thereby combining the aesthetic principles with a practical, functional structure that serves Khartoum’s ever growing infra-structure needs. Several challenges are handled during the design and construction stages;
Extreme Climate Conditions
Insufficiency of Construction Materials in Local Market
Difficulties in Transportation
Constrains of Floods in River Niles (The water level of the Nile rises by up to 6-8m)
Slow Bureaucracy
Insufficient Workmanship in Local Market

The noticeable advantages of steel were the most important factor to overcome the challenges of the project, not just as a structural system main component’s material;
Transportation of light steel elements (reduced transportation costs).
Fabrication of main bridge structural elements under quality control in Turkey (reduced the qualified workmanship need at project site).
Assembling the bridge elements with simple and clear procedures precisely (reduced construction errors with increased quality).
Allowing rapid construction (reduced time constrains).
The system easily satisfied the demands of aesthetic and sustainable design principles.
Reducing the superstructure mass, reducing the seismic forces as well as the dimensions of substructure elements accordingly (all means economy).
Reduction of the pile requirement (pile number, diameter, and length) influences the construction schedule positively, since the pile works are the most critical activities in construction schedule.
The Al Halfaia Bridge is mainly based on the use of advantages of the structural steel, hence the project budget could be reduced to very tight limits with a very limited construction schedule.

In February 2010, the Al Halfaia Bridge was officially handed over to the Owner. The bridge was completed under exceptionally difficult conditions in 23 months.
The precast formworks that allow the practical production of pile caps, use of trapezoidal steel sheet formworks hat provide a fast track slab construction, innovative design of steel superstructure, reduced the duration of the construction reasonably. It's notable that other concrete bridge constructions on the Nile are taking 4 to 5 years to complete (except El Mek Nimir Bridge).
In taking into consideration the benefits to Sudan economy, the integral type bridge has been chosen. Integral type bridges has been recognized and therefore used increasingly for the last 50 years all around the world.
The advantage of choosing a semi-integral bridge is minimizing expansion joints and expensive bearings which need higher maintenance costs. In especially developing countries and also sometimes in developed countries construction of integral bridges is a great advantage since regular maintenance is difficult to implement.
Transportation of the light steel superstructure to Sudan and easy assembly of steel elements, were the key strategies to realize low budget and challenging project on schedule. Steel was the greatest advantage with which to overcome the local constraints. The result is an aesthetic bridge complementing the beauty of River Nile.
Yapı Merkezi believes that the Bridge of the Al Halfaia; emphasizes innovative construction methods in steel composite bridge by reducing construction cost and time. Also this project successfully satisfies EU standards (Eurocodes), highlights abilities of semi-integral steel composite bridges in terms of quality and robustness.

Çelik Yapılar - Sayı: 24 - Ağustos 2010

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