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Repairing missile damageJanuary 2016

Baghdad missile-damaged building brought back to lifeNabeel A. Ibraheem Senior Structural Engineer, Ministry of Science & Technology; PhD Research Student, University of Technology, Baghdad, Iraq

IntroductionThe Al-Mansour Building (Figure 1) in Baghdad, Iraq, is a seven-storey office building designed and constructed by a consortium of three Japanese companies in 1982. Later, it was one of many buildings damaged in the 2003 war, when it was targeted by five smart missiles which drilled through its roof. Two of these missiles exploded within the second to third floors, while the other three continued punching through successive floors down to the basement, where they exploded. Severe damage was caused (Figure 2). Given the amount of column damage in particular, a redistribution of forces had clearly taken place to prevent total collapse. Survival was obviously aided by the absence of live load and removal of much of the concrete flooring weight.

Figures 3 and 4 show the main framing of the steel structure, identifying the worst affected location. This area included two main columns within the middle building plan, extending from the first up to the fourth floor, along with their surrounding main beams and joists (these originally supported concrete floors).

Rehabilitation proposalFollowing the war, many investigations had been conducted and proposals for repair submitted, but none were specific, practical or economical enough to be adopted. In late 2013, the author made a

floor beams. Many girders and joists, along with their concrete floor panels and steel decks, were also damaged in degrees ranging from slight to heavy.

The main strategy for rehabilitation was therefore removal of the two damaged columns followed by their replacement.To accomplish this, it was necessary to inset some temporary steel to bypass the damaged columns, and use this to transfer load down from the fourth to the first floor, and then to remove the damaged steel and replace it.

preliminary site visit, followed by a detailed survey, which recorded the damage to each steel member. This work was complemented by collation of all available technical reports and the original design calculations.

The explosion of missiles within the second to third floors of the building’s interior resulted in heavy damage to the surrounding area; the most severe was inflicted on the two main columns. These were virtually shredded, to an extent that prevented them from effectively supporting

SynopsisThis short article describes the rehabilitation of an office building in Baghdad damaged by a missile strike during the 2003 Iraq War. The author briefly sets out the damage to the building’s steel frame, explains how a structural model

• Figure 1 Al-Mansour

Building, Baghdad

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was created to enable the design of a supporting steel frame, and describes the installation of the temporary supporting frame and new steel columns using hydraulic jacks to raise the building’s upper stories.

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Based on the detailed site survey of the damaged steel frame, and working with the original design calculations, a structural model was prepared using STAAD.Pro. All existing components were represented whether damaged or not, but their actual condition was modelled. For example, some members were only partially damaged through their webs or flanges, so reduced section properties were considered appropriate. Techniques used included decreasing sizes or thicknesses, or introducing suitable intermediate releases to simulate any weakening that had taken place. Several structural models were prepared for the building to cover:

• the theoretical as-built steel frame• the existing damaged steel frame• the steel frame after eliminating the most heavily damaged members (i.e. from the first to the fourth storey)• the steel frame after introducing a supporting frame

Repair workThe restoration plan called for the introduction of a supporting steel frame through the void made by the explosion (three stories high), starting from the first floor and rising up to the fourth floor, to replace the load-carrying capacity of the damaged main columns (Figure 5). The supporting frame columns were laterally braced with square tubes at each floor level. Then, at the frame top, two hydraulic jacks were inserted to lift the upper building stories. This was necessary in order to introduce gaps at the contact points between the top of the damaged columns (i.e. above first-floor level) and the bottom of the new columns erected above, so that a steel plate could be inserted

"Given the amount of column damage in particular, a redistribution of forces had clearly taken place"

• Figure 2 Severe damage to interior steelwork

• Figure 4 View of most damaged steel framing where supporting steel

frame would later be placed (1st to 4th floors)

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Most damaged area

• Figure 3 Structural framing

arrangement identifying most damaged internal areas

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within the surrounding area. Structural calculations and analyses

showed that the minimum required jacking force required to lift the upper building floors was about 1500kN at each of the

two jacking points. Figure 7 shows the jacks in position and Figure 8 shows the renovated framing.

The lifting operation was performed in early 2015 and the upper (old) columns with their floors were lifted vertically by about 12mm at each of the two contact points using a hydraulic jacking force of 1100kN. A 12mm thick plate was then inserted between the column bearing end plates, and hammered in, before the pre-designed connection was fitted and welded. The last step was to release the hydraulic jacks so that the new replacement main columns became active and carried their share of load, restoring the integrity of the framing system.

firmly at the two positions. The connection was completed by bolting plates to the lower columns and welding the plates to the upper replacement columns (Figure 6).

The frame was designed to transmit forces from the upper floors (seventh to fourth) down to the undamaged part of the original main columns at first-floor level. Once the frame was installed, the damaged parts of the columns were dismantled; new columns were fabricated to measured lengths and inserted in place so that their tops just touched the original cut parts of the fourth-floor columns.

Many damaged steel members (girders, beams, joists) were also removed and replaced with newly fabricated members

January 2016

"The restoration plan called for the introduction of a supporting steel frame"

Existing columns retained

Damaged columns removed

Temporary frame

Beams to remain as part of the permanent structure but act as temporary restraints during rehabilitation

Two jacks

• Figure 5 Replacement steel

frame and load path

• Figure 6 Connections between old and new columns

(bolted on lower side, welded on upper side)

• Figure 7 Hydraulic jacks in position

• Figure 8 Renovated framing

Repairing missile damage

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