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Azarudin beam
- 1. GOVERNMENT ENGINEERING COLLEGE SEC. 28, GANDHINAGAR SUB.- MDID SUB. CODE- 2141907
- 2. Beam Design PREPARED BY HALA AZARUDIN I. (160133121010)
- 3. Beam Design
- 4. Beam Design • Beams are designed to safely support the design loads. • Beams are primarily designed for bending and shear. • Beam deflection must be checked. • Beams are sized to minimize material. Deflection
- 5. Steps in Beam Design 1. Establish the design loads 2. Analyze the beam 3. Select the preliminary member 4. Evaluate the preliminary design 5. Redesign (if needed) – Repeat the above steps as necessary to achieve a safe and efficient design 6. Design and detail the structural component
- 6. Stress • A measure of the magnitude of the internal forces acting between particles of the member resulting from external forces • Expressed as the average force per unit area = = Force F Stress Area A
- 7. Axial Stress • Tension and compression • Axial stress represented by Where F = applied force A = cross sectional area resisting load = F A σ
- 8. Axial Stress Example: Find the tensile stress of a 2 in. x 3 in. tension member subjected to a 45 kip axial load.
- 9. Strain • The change in size or shape of a material caused by the application of external forces • Axial strain, Where = change in length L = original length ε ∆ = L L ε
- 10. Strain Example: Calculate the strain if a 16 ft long structural member elongates 1.5 in. when subjected to a tensile load of 67 kips.
- 11. Stress and Strain • In many materials, stress is directly related to strain up to a certain point. Rise Run E == σ ε
- 12. Stress and Strain • Elastic behavior – material will return to its original shape when unloaded • Plastic behavior – material will retain some deformation when unloaded • Structural members are designed to act elastically during the service life of a building Yield Point
- 13. Factor of Safety • The ratio of the maximum safe load to the maximum allowable design load • Magnitude of the factor of safety varies depending on the loading conditions and type of forces induced
- 14. Allowable Strength Design (ASD) • Strength is related to stress – Strength indicates internal force – Stress indicates internal force per unit area • ASD limits the maximum internal force within a structural member • Maximum safe load = nominal strength – Internal force that causes yielding across the entire cross section • Maximum allowable load = allowable strength
- 15. Evaluation and Redesign Check Shear and Bending Moment By inspection, the plastic section modulus and web area for the W12 x 19 are larger than those for the W12 x 16 and are therefore sufficient to safely support the bending moment and shear. Use a W12 X 19
- 16. Beam Design
Editor's Notes
- Bending is the combination of tension and deflection that occurs along the beam when it is loaded. Shear is a force that acts perpendicular to the axis of the member, causing the internal particles of the member to slide against each other. Deflection is the amount of movement of a structural member under loading. Beam deflection is typically measured in inches. Deflection is limited by building codes. The maximum deflection is based on what the beam supports. For building materials, cost is generally directly related to the amount of material used. The more material (in other words, the more weight), the higher the cost. Designers typically attempt to reduce the weight of the construction materials to reduce cost.
- Structural design is an iterative process. You have already learned how engineers determine design loads, and you have analyzed beams for maximum shear and bending moment. Next, you need to select a preliminary member that you anticipate will provide adequate bending and shear strength with the least cost. This preliminary member must be evaluated to ensure that it will provide a safe and serviceable design. You may find that the chosen member does not provide enough shear strength or enough stiffness to adequately resist deflection. So you must revise your choice, always keeping the cost in mind. This will change the section properties used and may affect your loading calculations, which can require recalculation, reanalysis, and redesign. This process is repeated until you find a cost effective member that will be both safe and serviceable. The last step in the process is to document your design with construction drawings.
- When a beam is loaded, the internal fibers of the member must carry and transfer the resulting internal shear and bending moment to the beam supports. These internal forces result in internal stress in the member.
- Axial stress results from a force that acts along the length of the member. Tension (or pulling) and compression (or pushing) are axial forces or axial stresses. Tension stress and compression stress are represented by the Greek letter sigma.
- 1 kip = 1000 pounds
- Strain is also referred to as deformation. Axial strain is represented by the Greek letter epsilon. Strain is unitless or is recorded as inches/inch.
- If you have taken POE, you will recognize this stress-strain curve. We will design steel structural members. This graph shows the typical relationship between tensile stress (vertical axis) and strain for steel. As the tensile stress increases, strain increases. In fact, the relationship is linear until the material reaches its yield stress. At this point, the material begins to elongate much more quickly with respect to an increase in stress. The maximum stress that a material can carry is called the ultimate stress of the material. If a member is loaded beyond the ultimate stress, the material will begin to stretch very quickly (called necking) and eventually break at the fracture point. The slope of the linear portion of the graph is called the modulus of elasticity, or Young’s modulus, and is represented by a capital E. Each material has a unique modulus of elasticity. For steel, E = 29 million psi.
- The portion of the curve to the left of the yield point is the ELASTIC REGION. Material will behave elastically if the stress does not exceed the yield strength of the material. The portion of the curve to the right of the yield point is the PLASTIC REGION. Material will behave plastically if the stress exceeds the yield strength of the material. Although a member will not necessarily fail once it begins to act plastically, the excessive deformation is undesirable and can be dangerous.
- When designing a structure, the safety of the occupants is of the utmost importance, as well as protection of property. Many factors affect the behavior of a structure. As a structural engineer, you have little control over many of these factors For example, although you design the structure for a given load, there is no guarantee that the structure will not experience higher loads. Engineers can’t control the quality of the building materials used. What if a beam has a flaw that is not identified before it is installed? What if a construction worker fails to install all of the bolts in a connection and the error is not identified during inspection? A factor of safety is used to provide a comfort zone that can allow a margin of error for unforeseen circumstances that can adversely affect a building’s performance. The maximum safe load may be different depending on the design method used. We will use the allowable strength design method so that the maximum safe load is considered the load at which the member will reach the yield point. In other words, the maximum allowable load is set to a level well below the maximum safe load by a factor of safety. If the factor of safety is two, this means that the structure element must be designed so that the member is twice as strong as it theoretically needs to be in an ideal situation.
- Strength is another way to indicate stress. Strength is related to stress in that strength indicates an internal force, while stress indicates an internal force per unit area. Note: Two different members that have the same internal stress will not have the same internal force due to the differences in the cross section of the members. There are two standard structural design methods: Allowable Strength Design (ASD) and Load Resistance Factor Design (LRFD). Depending on the material, codes and standards may specify one or the other method. In some cases, which is true for structural steel, the engineer may choose the preferred method. We will use ASD for structural design in this class. ASD limits the maximum internal force that results from the design load combinations within a structural member. In ASD the maximum safe load is referred to as the nominal strength of a member. The nominal strength is the internal load that causes yielding across the entire cross section of the member. The allowable strength is the maximum internal force that can be induced in a member based on the design loads.
- Revisit your bending moment and shear calculations to make sure the plastic section modulus and web area are sufficient.