3.24 Incident CA—23 accountable to Professional Challenge
3.24.1 General
The aspect of dead load plays an important role in making the appropriate structural arrangement in the planning of any structure. It assumes still a greater importance while making an appropriate structural arrangement for locations falling in the most severe earthquake-prone zones such as zone V in India. The discussion planned under this subhead relates to higher span of beams, as required in the auditorium halls such the one for a cinema hall, for which the avoidance of intermediate columns becomes absolutely a functional necessity. The consideration of this aspect paused truly a professional challenge during my professional career as a structural designer. The challenges of this type were encountered in a number of cases of auditorium halls such as the ones of cinema halls. I had the fortune of designing a number of cinema halls in different cities/towns of Assam. The challenge was faced while planning and designing the balcony unit of these cinema halls. All of my clients for this type of assignments were private parties.
The first cinema hall planned and designed at my end was the one at the Dergaon town of Assam in the early parts of 1980s. The width of the hall was about 15 to 16 m. Naturally, the balcony required beams of span to the extent of 15 to 16 m, since no intermediate posts were desired for avoiding the obstruction of line of sight (to the screen) of the cinema-viewers sitting in the portion coming just under the balcony. Therefore, the beams required for the balcony slab along the width turned out to be of long span of the order of 15 to 16 m.The fact that I was then designing an RCC beam of such a long span for a structure to be built for the severe-mostearthquake zone of the country kept on striking my mind. The RCC beam so designed truly turned out to be a heavy one with appreciably high dead load. I knew very well that the most-preferred option to a structural engineer under such a situation ought to have been to go for a prestressed concrete beam. This alternative option appealed to me strongly, since by then, I had the experience of associating myself (in the capacity of a design engineer of M/s Engineering Consultants, India only for a short period) in the design of a prestressed concrete beam for an auditorium hall for a hotel in Delhi. In spit of this background, I eventually decided to go for the RCC beam in view of the fact that my client concerned was not so resourceful as to mobilise the men and machineries, as required for the construction of prestressed concrete beams.The execution was completed under my direct supervision. However, the tension accountable to heavy dead load of the RCC beam so constructed was always there in my mind. The sleepless night of the occurrence of the 1988 – Agust earthquake I had is still remembered very well. Next day morning I went straight to the Dergaon cinema hall and thoroughly checked if any stress/damage was caused by the earthquake on the heavy RCC beam of the balcony. Having seen no sign of any distress/damage on the said beam, I heaved a sigh of great relief and truly it was then and there, I decided not to design an RCC beam having the span to that extent any more during my professional life..
3.24.2 Balcony Floor of Bokakhat (Anandapur) Cinema Hall
After a few years, I got, for the second time the assignment of designing a cinema hall of similar type at Bokahat(Anandapur), Assam. The challenge similar to the one encountered in the design of the balcony even in this case crept in. However, as already decided after the agony I had during the night of the occurrence of 1988-August earthquake, I developed a technique of reducing the supported span of the balcony-beams. This technique consists in the structural system chosen for the balcony-slab, as schematically described through Figure 3.7.
The basic concept of the technique so chosen consisted of the structural arrangement through which the long span of 15 to 16 m of the beam CJ (Figure 3.7 (a)) was split into three smaller spans through the introduction of two intermediate supports at K and L, as shown in the figure. How to introduce these two intermediate supports without columns in the auditorium hall was, in fact the essence of the technique. This objective was achieved by providing overhangs (as cantilevers) namely GL and EK in continuation with beams FG and DE respectively. These two beams had monolithic supports at columns F/D and columns G/E (Figure 3.7 (b)).The cantilever parts GL and EK had spans of about 2.7 to 3m. These cantilevers were provided knowingly in violation of the code’s general recommendation of a maximum advisal cantilever-span of 1.5 m only in view of the absolute necessity of providing the intermediate supports to beam CJ for achieving the reduction in its unsupported span. This violation needed special attention in respect of designing and detailing these beams in addition to the necessity of execution under strict supervision. This was the reason for which I took a commitment from the client to the effect that the execution of all the critical structural elements of this structure would be done under my supervision. In view of the highest importance factor of the balcony floor, special attention was paid to the aspects of structural design and detailing including those for the joints at F, G, L, D, E & K.
A contractor having experiences in the execution of similar structures elsewhere was engaged by the owner and I personally kept on supervising construction of the salient elements including the balcony floor. I still remember a day on which I had the exchange of tough words with the so-called experienced contractor. During my checking of the reinforcements of the beams FGL & DEK, a lot of corrections in the laying of reinforcements were suggested to the contractor on the basis of structural drawings already provided to him. Being irritated on my suggested corrections, he reacted by passing a comment going as — ‘Sir, you are providing a lot of reinforcements on these parts of beam (GL & EK in Figure 3.7 (a))’. I did not get angry on hearing his comment, since by then I got used to facing a number of situations created at sites by factors primarily accountable to ‘A little knowledge is a dangerous thing’. Even then, I failed to resist my temptation of asking him a question (as I used to ask my students inside the class room) —- Do you know the supporting conditions of these spans of the beam? As expected, he answered —I do not know that, Sir. But I constructed many balconies. I closed the discussion on this issue with a sincere advice to him as—-Your experience is appreciable though you are understandably not aware of the technical knowledge and skill, which are required for design and preparation of the detailed structural drawing. So, please keep it in mind always that you have to execute the work perfectly in conformity with the structural drawings given to you under the guidance of the supervising engineer. This approach has to be duly honoured by you to ensure the quality of construction, as conceived by the designer during the phases of planning and design of the structure. He eventually followed my advice and completed the work successfully.This type of situations normally occurs at the site of many constructions in today’s construction industry. To face a situation of this type, the engineers of the younger generation have to equip themselves with the basic understanding of the structural drawings apart from basic knowledge and skills about different aspects of quality control of different materials and workmanship in relation to code- provisions. As and when necessity arises, the site engineers concerned are expected to consult the designer of the structure. These aspects have been duly discussed in greater details in my book9. This cinema hall has been more than 30 years old by now and hence it withstood efficiently the occasional loads caused by a number of earthquakes such as the one of 2021. The provision of the beams (FGL & DEKin Figure 3.7 (a))) yielded another advantage of converting the slab panels of the balcony into two-way ones. The balcony steps of the required dimensions based on the appropriate clearance for the line of sight to the screen (as seen in Figure 3.7 (a)) were made of plain cement concrete.
The present view of this cinema hall is shown in Image 3.13 below.
3.25 Concluding Remarks
While coming to the end of my professional life in this period ‘C’ (as defined in Figure 1.1), a series of events naturally come to my mind. It is not possible to deal with all of those events of this period in the pages of a single book, since I have yet to cover many more significant incidents covered under the period 1982 to 1996 (included in both the Parts Cand D of Figure 1.1). The salient aspects of the different challenges encountered in the pursuit of my professional life as an Editor of the technical news record called ‘The Construction Tribune’ are being discussed in the next Chapter of this book (now in the process of writing). This part has been identified and marked as Part CD in Figure 1.1 for the obvious reason. All the articles to be written for this Part CD will also go on being published in this blog for the objective briefly stated earlier.
(To be continued in the next Post of this Blog)
References:
9. A book entitled ‘A Journey through the Construction Industry’ by Dr. H. K. Barua, May, 2025, Excellar Books (Global Press), Kalkota, W.B.