Deep Beam Design Based on ACI Code PDF

Libyan Academy for Postgraduate Studies Department of Civil and Architectural Engineering/ Structural Engineering Course: Advanced Reinforced Concrete Design- A(CES605) Lecture (3): Deep Beam Design Based on ACI Code...

Libyan Academy for Postgraduate Studies Department of Civil and Architectural Engineering/ Structural Engineering Course: Advanced Reinforced Concrete Design- A(CES605) Lecture (3): Deep Beam Design Based on ACI Code ********************************************************************* 1- Introduction to Deep Beams According to ACI 318, a deep beam is a structural element in which clear span to depth ratio (L/D) is less than 4 for simply supported beams and less than 5 for continuous beams also when concentrated loads exist with a distance 2h from the face of the support. Deep beams are presented in the ACI-318-08 standard in Section 10.7. They are defined as members that are loaded on one face and supported on the opposite face such that strut-like compression elements can develop between the loads and supports. - Deep beams behavior is not governed by flexure only and considerations of combined shear and flexure need to be addressed to properly analyze and design deep concrete structural members. The Finite Element Methods (FEM) and the Strut-and-Tie Model (STM) are the two primary methods defined in the ACI 318 standard for deep beam analysis. - Applications: Deep beams are commonly used in transfer girders, bridge piers, foundation walls, and water tanks. They are essential in structures where high loads are transferred over short spans. As an example, deep beams commonly exist in reinforced concrete structures as framing members spanning between columns. In a typical building frame as shown below deep beam commonly serve as transfer girders to transfer heavy concentrated loads from one or more columns discontinued at certain elevation. Deep Beam serve as transfer girder Similarly, in pile supported deep foundations (pile caps) deep mat slabs are supported on closely spaced piles to transfer heavy column loads to bed rock or stable soil layers. Deep Beam serve as transfer girder to supported deep foundations (pile caps) Deep beam with opening 1 /2 Best luck folk Spring (2023-2024) Dr. Mohamed karim  Libyan Academy for Postgraduate Studies Department of Civil and Architectural Engineering/ Structural Engineering Course: Advanced Reinforced Concrete Design- A(CES605) Lecture (3): Deep Beam Design Based on ACI Code ********************************************************************* Handout sheet as lecture material regard to Strut-and-Tie Models 2- Strut-and-Tie Model (STM): Unlike slender beams, deep beams transfer loads primarily through a combination of direct compression struts and tension ties. This means that deep beams exhibit a nonlinear distribution of stresses, particularly shear stresses. Moreover, The Strut-and-Tie Model is a design methodology recommended by ACI 318 for structures, particularly deep beams, where traditional beam theory does not apply due to complex stress distributions. STM is based on representing a structure or a structural component as a truss-like system composed of compressive elements (struts), tensile elements (ties), and nodal zones where these elements intersect. Key Concepts of STM I- Struts are the compressive members in the model, representing the zones of concrete that carry compressive forces, Struts are responsible for transferring load from the applied forces to the supports; there are two types of struts. Prismatic Struts: Constant cross-section throughout their length. Bottle-shaped Struts: Wider in the middle, representing the spreading of compression forces. II- Ties: are the tensile members in the STM, represented by reinforcing steel bars. Ties resist tensile forces and are essential to balance the compressive forces in the struts. These ties act as reinforcement in regions where tensile forces are present, such as at the bottom of beams or near supports. III- Nodes: Nodes are the points where struts and ties meet and where loads or reactions are applied. They are critical regions and must be designed to resist high local stresses from the intersecting members. there are three types of Nodes: o C-C-C Node: Three compressive struts meet. o C-C-T Node: Two compressive struts and one tie meet. o C-T-T Node: One compressive strut and two ties meet. 2 /2 Best luck folk Spring (2023-2024) Dr. Mohamed karim