STUDIES ON THE DEVELOPMENT OF ECONOMICAL DRAINAGE SYSTEMS FOR MULTI-STOREYED BUILDINGS

Abstract

The thesis presents results of an analytical investigation carried out with a view to formulating rational design procedures for economical drainage systems in multi-storeyed buildings, thus obviating the limitations of semi-empirical design procedures presently invogue. Specifically the systems investigated include the 'Single Stack' (SS) and the 'Modified One-Pipe' (MOP) systems that have proven economical advantage over the conventional 'Two-Pipe' and 'One-Pipe' systems of drainage. The analytical models have been validated through experimental data collected on full scale multi-storey test rig facilities. An excellent correlation between the negative pressures predicted by the analytical models and those recorded experimentally for both the systems brings to the fore the utility of such analytical models for design of drainage systems in multistoreyed buildings. The design of building drainage systems essentially requires fixture/discharge unit-simultaneous flow relationship in order to estimate the probable hydraulic loading on the system during the peak hours of operation. The present designers rely on data provided in the National Building Code (India) which is derived from the U.S. National Plumbing Code (NPC) and the British Standard Code of Practice (BSCP). The need for collecting relevant data under Indian conditions of ii water supply and usage, and sanitary appliances' characteristics, can hardly be over-emphasised for realistic designs. The present study accordingly addresses itself to the task of deriving discharge unit - simultaneous flow relationships in residential and office buildings with recourse to data collected in Delhi. Loading weights in terms of discharge units assigned to various sanitary appliances in such buildings based on flow-characteristics, and frequency and probability of their usages have been found to be markedly different than those incorporated in the NBC, an also the discharge unit-simultaneous flow relationships. An endeavour has also been made to identify the fallacies in conventional design procedures for drainage systems based on limiting capacities of stacks. Preliminary investigations on SS-system brought out the need for the consideration of existing suction in the drainage stack for simulating actual situation in tall buildings. Such a consideration indeed yields limiting capacity values in close agreement with those predicted by the analytical model. The underlying assumption, in the preparation of vent sizing tables incorporated in the NPC and BSCP(that form the basis for vent design in India), that most of the air in the vented drainage system is carried by the vent stack, has been put to test in the present investigation, The results reveal that, contradictory to the afore-mentioned assumption, a major proportion of air is supplemented through the main drainage stack thus warranting modification in the design methodology iii for vented systems. The limiting capacity of MOP - System predicted by the analytical model incorporating this modification compares well with the values recorded on the test rig. The horizontal branch connecting the sanitary appliances to the drainage stack provides the most vulnerable component for the development of negative pressure due to self-siphonage (caused by full-bore discharge condition resulting in water seal loss from traps of appliances). This part of the system, therefor?, plays as important a role as the main drainage stack in ensuring functional efficacy of building drainage systems. Accordingly a detailed experimental investigation has been undertaken to derive design relationships for horizontal branches in residential and commercial buildings. Faulty design of plumbing systems is one of the many causes for defunct water supply and waste water collection systems in India. A case in point is the discharge unit ratings considered for design of plumbing systems for water supply and drainage. Several such fallacies in the conventional methods of design have been identified in the present investigation with appropriate corrective measures. The analytical models presented in this work provide a simple, straight-forward and rational tool to the designer obviating fallacies in the conventional design procedures and the need for expensive and time-consuming experimental trials on full scale test rigs.