Experiments have shown that as the depth of the beam increases, the intensity of shear stress decreases especially in lightly reinforced beams. This phenomenon is referred to as “size effect”. Shear strength is not constant as given by some design codes like the ACI. To understand size effect, an artificial neural network (ANN) model was developed for RC beams without stirrups which fail under diagonal tension.
The ANN model consists of five input nodes representing (1) the compressive strength of concrete, f’c, (2) beam width, b, (3) effective beam depth, d, (4) shear span to depth ratio, a/d, and (5) longitudinal steel ratio. The output is the shear stress, Vu/bd. The graphical user interface of the Visual Basic program of the ANN model is shown.
The figure shows the simulation where the depth (d) was varied from 20 cm to 100 cm for two values of f’c and a/d and constant values for b at 15 cm and r at 2.75%. The size effect is obvious where the shear stress decreases with increasing depth. The experimental results by Kani shows a similar trend as the model. The shear stress also depends on the shear span to depth ratio – a shorter beam (a/d = 2.5) has a larger shear strength than a longer beam (a/d = 5.0).
How safe our our large RC beams with respect to shear failure? Structural engineers must take note of the decrease in shear strength of concrete for large beams so that they can provide adequate shear reinforcements or stirrups.
Reference: Oreta, A.W.C. (2004). "Simulating size effect on shear strength of RC beams without stirrups using neural networks." Eng'g Structures 26(2004) 681-691, Elsevier.
Jeopardeng by C. Fabie and R. Masa: This is an adaptation of the famous American game Jeopardy. The game has four different categories that cover various topics about civil engineering. Each category has four objective questions. There is a data base of questions which are selected randomly. The user answers all questions under the four categories in any order, aiming to bag a high score. After all questions have been answered within the time limit, the user is prompted to the “Final JeopardENG Round”; wherein a computational question will be asked to the user worth 5000 points.
Dr. Naveed Anwar is the Associate Director of ACECOMS and an Affiliate Faculty of the School of Engineering and Technology of the Asian Institute of Technology, Bangkok, Thailand. Dr. Naveed is the principal author of several engineering software including SDL, GEAR, SYSDesigner. He is also a consultant of CSI, the developer of ETABS, CSI Col, SAFE and SAP2000.
Prof. Emeritus Per Tveit, Dr. Ing. of Agder University, Norway, visited De La Salle University, Manila a few years ago to share his knowledge and expertise about Network Arches. "When I was a student over 50 years ago, I got the idea of the network arch. Optimal network arches are arch bridges where some hangers cross other hangers at least twice. When the arches are less than 18 m apart, the tie should be a concrete slab with partial longitudinal prestress. The arches should be universal columns or American wide flanges. Network arches are best suited for spans between 80 m and 170 m, but will compete well in a wider range of spans. This results in attractive bridges that do not hide the landscape behind them. A network arch bridge is likely to remain the world’s most slender tied arch bridge, " he says. Indeed, Tveit can be considered the "father of network arches." He traveled around the world using his own resources spreading the information about network arches - the basic components, analysis, design and construction. His website has detailed information about network arches. 
