building designer letter

i am writing in regards to the proposed changes to the use of the building, which suggest using ground floor area as a theatre. the proposed change would cause significant changes in the design, increasing the length of a central span to 13 meters and reducing the side spans to 5 meters. these are major changes that would mean having to re-do the whole design of a floor and carry out new calculations as a designer i would like to advise on the list of additional steps that calculations as a designer i would like to advise on the list of additional steps the design team would need to undertake in order to make changes to the project 

· Re-designing the whole building structure from beginning including the change of foundation due to different loads, but also changes in the sizes of beams, columns and floor slabs.

· choosing appropriate dimensions for long span beams, which can carry extra loads from building structure, the internal beams and columns dimension would have to be increased to provide space for bigger reinforced steel bar diameters and increase the number of bars. using general sizing rules such as span to depth ratios, according to Eurocode2. the dimensions of the member are adjusted if the section is either under-strength or significantly over-strength, or if the serviceability or any other limit state is exceeded.

· choosing concrete of higher strength properties.

· the larger long-span of central beams will affect the central columns dimension to be more thick than before

· the beam thickness need to be increased to carry more loads from extended beam 

· the floor slab system has to be re-assessed, due to the changes in loads, the two best options for floor slabs above the theatre are:  

· A_ the baffle slab- with the use of this slab it would be possible to maximize the column-free spaces, as per requirement.

· b_PT floor slab- with these the maximum span of 24m is possible and it helps to reduce the number of columns  

Overall, the changes at this stages of the construction project are still possible, however, i would like to stress the cost implications that are assiciated with it. now that we have completed the design we would require additional time to mae changes- this means an overall delay in delivering the project. as the construction phase cannot start until the new design is completed this obviously creates a risk of financial loses furthermore it is risky to make changes at this point, as the whole structure has been designed for a building of a different use, now the loads on the ground floor would significantly change , but also by moving the columns we move the crucial support to the above structure, although it is possible to carry out additional calculations it is now easier to miss out on factors that can influence the structure, that we didn’t previously had to take into account- it is easier to design it for the building for a specific purpose from the beginning than having re- design it for a different one at the end , finally the change you are proposing will make the design more complex and will increase the overall cost of the structure, such as with the need to use different materials and technologies.

i can confirm it would be possible for us to apply changes to the project, however taking all the above into account, i would advise to reconsider the decision and see which option you would find more beneficial