Structural analysis of beams and frames is fundamental in architectural design to ensure the safety and serviceability of buildings. In Kenya, where diverse building types range from low-rise residential to complex commercial structures, understanding how loads affect beams and frames is crucial for architects collaborating with structural engineers. This chapter develops practical skills in analyzing forces and moments in beams and frames, enabling architects to make informed decisions during design and coordination phases.

2.1 Forces on beams application

Beams are horizontal structural elements that carry loads from floors, roofs, or walls and transfer them to columns or walls. In architectural contexts such as hospitals, schools, or county offices in Kenya, beams must be designed to safely resist bending, shear, and axial forces caused by imposed loads. Accurate determination of forces acting on beams allows architects to specify appropriate beam sizes and materials, ensuring structural integrity and compliance with Kenyan building codes.

2.1.1 Types of forces acting on beams

Beams primarily experience the following forces that influence their design:

• Bending Moment: The internal moment generated by external loads causing the beam to bend.
• Shear Force: The force that acts perpendicular to the beam's axis, causing sliding failure between sections.
• Axial Force: Though less common in beams, axial forces occur due to compressive or tensile loads along the beam's length.
• Distributed Loads: Loads spread continuously over a length of the beam, such as floor finishes or roof loads.
• Concentrated Loads: Point loads applied at specific points, such as heavy equipment or column reactions.

2.1.2 Load types on beams in architectural structures

Architectural beams are subjected to various load types depending on building use and design:

• Dead Loads: Permanent loads including the self-weight of the beam, fixed finishes, and structural elements.
• Live Loads: Variable loads such as occupants, movable furniture, and temporary equipment.
• Environmental Loads: Wind, seismic, or snow loads that may induce additional forces on beams.
• Impact Loads: Sudden forces from dynamic activities like machinery operation in industrial buildings.
• Settlement Loads: Forces due to differential foundation settlement affecting beam support reactions.

2.1.3 Support conditions and their effect on beam forces

The way a beam is supported directly influences the internal force distribution:

• Simply Supported Beams: Supported at both ends-free to rotate but not translate vertically, inducing bending moments and shear forces.
• Fixed Beams: Ends are restrained against rotation, producing higher moments near supports but reduced midspan moments.
• Cantilever Beams: Fixed at one end and free at the other, experiencing tension on the upper fibers and compression on the lower fibers.
• Continuous Beams: Span over multiple supports, resulting in complex moment and shear distributions.
• Propped Cantilever: Combines cantilever action with a simple support to reduce deflections and moments.

2.1.4 Applications of beam force analysis in architectural design

Understanding forces on beams helps architects in:

• Selecting beam sizes and materials: Ensuring beams can resist calculated forces safely.
• Coordinating with structural engineers: Providing initial load assumptions and spatial requirements.
• Planning beam placements: Avoiding clashes with architectural elements like ducts and finishes.
• Detailing beam connections: Specifying supports and connection types suited to force conditions.
• Cost estimation and optimization: Balancing structural safety with economical design solutions.

Chapter Summary

This chapter focused on the application of forces on beams, highlighting how external loads affect beam behavior in structural systems. It explained the calculation of forces on both beams and frames using fundamental techniques, starting with the method of section which involves cutting through structures to analyze internal forces. The method of joint was presented as a way to solve forces at the connection points of frame members by considering equilibrium. The moment area method was introduced as a tool for determining beam deflections and slopes by analyzing the area under bending moment diagrams. Additionally, the chapter covered the preparation of force moment drawings, essential for visualizing and understanding the distribution of moments along structural elements. Together, these principles and methods enable accurate analysis and design of beam and frame structures in civil engineering practice.