--- title: "Types of loads on structures and effects" subject: "Mechanics of Solids" chapter: 1 key: "semester_5/mechanics_of_solids:loads-on-structure-effects" source: https://www.bctengineer.com/q/semester_5/mechanics_of_solids/loads-on-structure-effects site: BCT Engineering --- # Types of loads on structures and effects Mechanics of Solids · Chapter 1: Load on Structure and Response of Material - Asked in: year not given, 5 marks - Video: [TYPES OF LOADS USEFUL FOR SFD AND BMD DIAGRAM | STRENGTH OF MATERIALS](https://www.youtube.com/watch?v=2NO4eKXfZ_8) — TIKLE'S ACADEMY - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/mechanics_of_solids/loads-on-structure-effects - Whole chapter: https://www.bctengineer.com/md/semester_5/mechanics_of_solids/chapter-1 ## Question Classify the loads that act on a structure. Explain the effect each kind of load produces in a member. ## Short answer Loads are classified by duration (static, dynamic, impact), permanence (dead, live), and distribution (point, UDL). Axial load causes normal stress σ=N/A; transverse load causes shear and bending stress σ=My/I; torque causes torsional shear τ=Tr/J; restrained thermal expansion causes thermal stress. ## Answer A **load** is any external action (force, moment, pressure, temperature change, support settlement) that makes a structure deform and develop internal stresses. Loads are classified in more than one way. #### Classification of loads | Basis | Types | Examples | |---|---|---| | Duration / variation with time | Static, dynamic, impact, cyclic (fatigue) | Self weight; machine vibration; falling weight; rotating shaft | | Permanence | Dead, live | Self weight of beam; people, vehicles | | Environmental | Wind, snow, earthquake, thermal | Wind on a tower; temperature rise in a rail | | Distribution | Point, line (UDL, UVL), surface | Column on a beam; slab on a beam; water pressure | - **Static load**: applied slowly, so inertia forces are negligible. - **Impact load**: applied suddenly with kinetic energy, so stresses can be several times those of the same static load. - **Cyclic load**: repeated many times; failure can occur below the yield stress (fatigue). #### Effect of load on a member The effect depends on how the load acts relative to the axis of the member. | Load | Internal action | Resulting stress | Example | |---|---|---|---| | Axial (tension or compression) | Normal force $N$ | $\sigma = N/A$ | Tie rod, column | | Transverse (shear) | Shear force $V$ | $\tau = VQ/(Ib)$ | Rivet, beam web | | Transverse load or couple | Bending moment $M$ | $\sigma = My/I$ | Floor beam | | Twisting couple | Torque $T$ | $\tau = Tr/J$ | Transmission shaft | | Internal or external pressure | Hoop and axial stress | $\sigma_\theta = pr/t$ | Boiler shell | | Temperature change | Thermal strain | $\sigma = E\alpha\Delta T$ if restrained | Bridge deck | In practice members carry **combined loading**, for example a shaft in bending and torsion, or an eccentric column in compression and bending. The stresses are then found for each action separately and combined by superposition, valid for linear elastic response and small deformation. The combined stress state is then examined with the stress tensor to find principal stresses and check failure. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why can an impact load produce stresses several times those of the same static load? A. It is applied suddenly with kinetic energy, not slowly B. It acts for a longer time C. It is always a point load D. It changes the material's E Answer: A. An impact load is applied suddenly and carries kinetic energy, so inertia effects are not negligible and stresses exceed the static value. (Key point: Impact vs static load) 2. What is the key danger of a cyclic load? A. Failure needs stress above the ultimate strength B. Failure can occur below the yield stress after many repetitions C. It only causes temperature stresses D. It acts only on the web of a beam Answer: B. Repeated loading causes fatigue, so a member can fail at stresses below yield. (Key point: Cyclic load and fatigue) 3. A transmission shaft carries a twisting couple. Which internal action and stress formula apply? A. Bending moment M, sigma = My/I B. Normal force N, sigma = N/A C. Torque T, tau = Tr/J D. Shear force V, tau = VQ/(Ib) Answer: C. A twisting couple produces torque T and shear stress tau = Tr/J. (Key point: Load action and stress) 4. How are stresses from combined loading (e.g. bending plus torsion) found? A. Use only the largest single action B. Average the stresses of all actions C. Find each separately and superpose, valid for linear elastic and small deformation D. Multiply the stresses together Answer: C. Each action is analysed separately and the results are superposed, which is valid for linear elastic response and small deformation. (Key point: Combined loading) ## Related in Mechanics of Solids - [Bent bracket deflection by unit load method](https://www.bctengineer.com/question.md?key=semester_5%2Fmechanics_of_solids%3Abracket-deflection-unit-load) — Mechanics of Solids, chapter 5 ## Related in other subjects - [Truss member forces with 25, 50, 10 kN loads](https://www.bctengineer.com/question.md?key=semester_1%2Fapplied_mechanics%3Atruss-forces-25kn-50kn-10kn-hinge-roller) — Applied Mechanics, chapter 7 - [Member forces of truss with 20 and 10 kN loads](https://www.bctengineer.com/question.md?key=semester_1%2Fapplied_mechanics%3Atruss-forces-20kn-10kn-12m-8m) — Applied Mechanics, chapter 7 - [Project financing; structures; capital structure steps](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aproject-finance-define-structures-steps) — Project Engineering, chapter 6 - [Lateral load effect on wall with and without opening](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Alateral-load-wall-with-openings) — Concrete Technology and Masonry Structure, chapter 9