Strut and tie modelling of deep beams

Abstract

This study creates a spreadsheet program in order to analyse strut-and-tie models that can be used in different kinds of deep beam configurations. The spreadsheets can help to perform quick calculations to obtain the beam capacity without the need to perform manual calculations. The analysis of deep beams in the spreadsheet is based on Eurocode 2(EC2) and ACI-318 code. The results are then compared to published test results. Two spreadsheets were created in this project. The first spreadsheet focuses on the analysis of simply-supported single-span deep beams with only one concentrated point load at the middle span, while the second spreadsheet focuses on the analysis of simply-supported single-span deep beams that are loaded with two symmetrical point loads at different shear span distances. In order to obtain the beam capacity, backward calculation is performed by inputting the amount of reinforcement after the strut-tie model (STM) is created. There are a total of six specimens used for single point-loaded deep beam group and thirty four specimens used for deep beams group which are loaded by two symmetrical point loads. Twenty two out of thirty four specimens are deep beams with a fixed beam depth but different shear span lengths. The remaining twelve deep beams are specimens with different beam depths, shear spans and main steel contents. The results showed that there are a few parameters that govern the strength of deep beams. Angle between strut and tie of the model and shear span can greatly affect the effective strength of struts. As angle between strut and tie decreases, beam capacity decreases. Beam capacity of the deep beams which failed by diagonal splitting are found to be overestimated. This can be the limitation of EC2 and ACI code in designing strut tie models for deep beam which has the tendency to fail in diagonal splitting failure mode.