Seismic retrofitting methods for the jack arch masonry slabs

Jack arch masonry slab, developed in the post-industrial revolution Britain has been used extensively to floor and roof industrial and residential buildings in many parts of the world. It is still in use in parts of Europe, the Middle East and Indian subcontinent. Collapse of a large number of these composite slabs during past earthquakes, including those belonging to some buildings of historic importance, has pointed out the weakness of this type of flooring to seismic loading. It has also highlighted the need for developing appropriate retrofitting schemes. Two different retrofitting methods are currently in use. One method uses a thin reinforced concrete layer over the slab to provide integrity and the necessary strength. Another method utilizes transverse beams to form a steel grid with the main beams to achieve the same objectives. In this paper, out-of-plane pushover tests are first conducted on a number of full-scale ordinary and retrofitted jack arch slabs. Results of the tests are then used to compare the strength capacity and other seismic performance parameters of the slabs including; ductility and the behaviour factor. Numerical analyses are also carried out in support of the experimental investigation. It is concluded that the steel grid method of retrofitting, in addition to being easier and faster to perform and much less costly, addresses all the strength and performance requirements of the slab, whereas, the concrete layer method, though effective in increasing the strength, considerably increases the weight of the slab, which, in turn, may increase strength demand on other structural elements. The benefits of using the concrete layer in improving the seismic performance are also less than those of the steel grid method.

► Three different methods of seismic retrofitting jack arch slabs are investigated.
► Tie-bracing method does not provide the required integrity and strength.
► The concrete layer method is the most invasive and the least cost-effective.
► The two-way steel grid method is less invasive and the most cost-effective.