Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Passive Fire Protection II Lec 11-Assessment and repair of fire- damaged structures Dr. Zayed Al-Hamamre

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Introduction  Often the initial response when looking over a fire-damaged structure is one of despair and horror at the extent of damage.  This situation is exacerbated (made worse) by the amount of non-structural debris (rubbish) lying around together with the acrid (bad) smell of many combustion products.  Immediate decisions must be taken on the short-term safety of the structure and whether any temporary propping is necessary or, indeed, whether some demolition work is necessary.  This decision will often need to be taken very quickly after the fire and will generally be based on a visual survey and expert judgment.  The assessment of fire damaged structures is very much a ‘black art’ in that it relies heavily on experience.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel |  It is also to be noted that it is at this point that the owner’s, or occupier’s, insurance company will become involved, as even if the structure is capable of being saved,  It will be a matter of economics as to whether there should be repair or demolition and complete rebuild.  This question can often be answered after a thorough visual inspection has been carried out. Visual inspection The aim of the visual inspection is to determine: 1.The short-term stability of the structure and 2. The extent and severity of the fire.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Stability The original drawings for the structure should be consulted at this stage.  These allow assessment of how the structure transmits the applied loading and enables the principal load carrying members to be identified, as well as those providing structural stability.  The inspection needs to check any excessive deformation, deflection or cracking in the main load-carrying members and integrity at the connections between the main members.  It is also necessary to consider the stability if excessive bowing has occurred in any masonry cladding or internal compartment walls.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel |  In the case of concrete construction, attention should be given to damage due to spalling on beams and columns as this may reduce the load-carrying capacity of the member due to excessive temperature rise in any reinforcement.  Where the fire has only affected part of the structure, it is essential that the inspection also extends to any part of the structure not damaged directly by the fire; it is possible that a substantial redistribution of forces can occur into the unaffected part of the structure

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel |  Moments in concrete frames remote from the fire affected compartment exceeded the design moments,  The structure behaved during the fire in a totally different manner to the way it was designed, in that forces were redistributed away from the fire by columns acting in tension to transmit forces to the relatively cool upper stories of the structure. o Moments in concrete frames remote from the fire affected compartment exceeded the design moments, o The structure behaved during the fire in a totally different manner to the way it was designed, in that forces were redistributed away from the fire by columns acting in tension to transmit forces to the relatively cool upper stories of the structure.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Estimation of fire severity 1.The first method of obtaining a rough estimate of the fire severity is by: o The use of the fire brigade records in terms of the number of appliances called out, o The length of time taken to fight the fire, o The length of time between the fire being noted and the arrival of the brigade, o The operation of any automatic fire detection or fire-fighting equipment and o The degree of effort required to fight the fire.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | The second approach is to estimate the temperature reached in the fire by a study of the debris caused by the fire. o It is thus important that no debris is removed until such a study is carried out; otherwise, vital evidence may be lost. o Provided the materials generating the debris can be identified, the knowledge may be used to give an indication of temperature reached, since most materials have known specific melting or softening temperatures; some typical data are given in the following table. o Care should, however, be exercised when using these data as the temperature varies over the height of a fire compartment, thus the original position of a particular artefact is important. o Also, this method only gives an indication that particular temperatures were reached and not the duration of exposure to that temperature.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel |

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | A third method that is available to give an estimate in terms of either the standard furnace test duration or a known fire, is to measure the charring depth on any substantial piece of timber known to have been exposed to the fire from the start of the fire. o The charring depth can be related back to the standard furnace exposure since timber of known, or established, density can be assumed to char at a constant rate between 30 and 90 min standard exposure.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel |  A fourth method is to calculate the fire severity from estimates of the compartment size, the fire load density and the area of openings (ventilation factor)  It should be remembered that these equations assume the whole fire load ignites instantaneously and that the whole ventilation is available from the start of the fire, and thus may not be totally accurate for a large compartment fire.  In practice, no one of the above methods is completely reliable and therefore a combination of methods must be used to give a reasonable answer.  The visual inspection, once carried out, will have identified those areas which must be either immediately demolished (where the damage is beyond that capable of being repaired) or those areas which may be capable of being repaired if sufficient strength can be attained.  The inspection will also identify where there is no, or only very superficial, damage. This last category merits no further discussion.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel |  If repair is considered feasible, then a much more thorough investigation is required to ascertain the exact extent and severity of any damage and the residual strength of the structure.  To do this, it is first necessary to clear all debris from the structure and to clean as much smoke damage as possible to allow an unimpeded examination of all surfaces.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Damage assessment  This needs carrying out in a series of stages: o The first stage involves a complete fully detailed survey of the structure. o The second stage ascertains the residual strength of both the individual members and of the complete structure. Structural survey  For all structures, the first stage is to carry out, a full line and level survey.  This is needed to assess the residual deformations and deflections in the structure.  The measured deflections should be compared with those for which the structure was designed.  Care should be taken to note the effect of any horizontal movements due to thermal actions during the fire.  Such effects of horizontal movement are often apparent away from the seat of the fire.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel |  In concrete structures, o It is necessary to note the existence of spalling and therefore exposed reinforcement. o It should be noted that large amounts of spalling do not necessarily imply that the reinforcement, or the structure, is substantially weakened since spalling may occur late in a fire due to the action of cold water from firemen’s hoses. o It is likely that where the exposed surfaces are smoke blackened, spalling occurred early in the fire. o It is useful to note the colour of the exposed concrete face as this can give an indication of the temperature to which the element was exposed; o Care is needed, though, because spalling may nullify the observation, and some aggregates do not exhibit colour changes.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | o Note should also be made of the formation of cracks. o Cracking is unlikely to be deleterious in the tension zones of reinforced concrete beams, but will indicate the existence of severe problems should it occur in the compression zones of beams or slabs or in columns. o The fire test on the concrete frame at Cardington demonstrated the ability of that particular frame to remain intact in spite of large degrees of spalling, o But it also suffered large horizontal deformations at the top of the fire test compartment

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | In steel structures,  Most structural steels regain more strength on cooling  There will be a slight loss in strength.  However, the resultant deformations are likely to indicate the state of the structure.  It is important to assess the integrity of the connections;  It is possible that bolts could have failed within the connection or could have become unduly deformed.  Where the floors comprise profile sheet steel decking and in situ concrete, examination should be made for any separation between the decking and the beams.  This separation can still occur even if thorough deck stud welding was used.  Another potential point of failure is the shear bond between the decking and the in situ concrete.

Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel | Chemical Engineering Department | University of Jordan | Amman 11942, Jordan Tel |  Even with substantial damage of the types mentioned above, the structure may still be intact as demonstrated after the fire tests on the steel frame structures at Cardington.  Masonry is either used in low-rise load-bearing structures or as cladding to framed structures.  The major cause of distress to masonry walls is expansion or movement in the structure caused by thermal action on the frame or flooring.