**Types and Characteristics of Timber Roof Trusses**:
– Top members: top chord, bottom members: bottom chord, interior members: webs.
– Types: closed trusses with horizontal bottom chord, open trusses with raised bottom chords.
– Closed trusses: with a tie beam or hidden by a ceiling.
– Open trusses: interrupted tie beam or visible roof framing.
– King post truss components: king post, tie beam, principal rafters, struts.
– Queen post truss components: queen posts, tie beam, straining beam, principal rafters.
– Liegender Stuhl truss: origin, structural features, and comparison with Stehender Stuhl truss.
**Structural Aspects and Development of Timber Roof Trusses**:
– Development in medieval times.
– Balancing lateral forces for stability.
– Factors causing lateral forces: wind, flexibility.
– Purpose of tie beams in closed trusses.
– Structural requirements for king post trusses.
– Extension of span with queen post trusses.
– Use of iron rods in queen post trusses.
**Evolution of Wooden Truss Connections**:
– Early connections: mortise-and-tenon joints.
– Issues with unseasoned posts and shrinkage.
– Off-center holes for structural behavior.
– Use of pegs to pull posts together with gravity.
**Notable Structures and Architectural Styles Related to Timber Framing**:
– Bent (structural) and reciprocal frame.
– Truss bridge and Palladian architecture.
– Architectural significance of queen post trusses in Italy.
– Use of Liegender Stuhl truss in 18th and 19th-century German settlements in the U.S.
**Technical and Historical Influences on Wooden Trusses**:
– Permanent bracing design for MPC wood roof truss webs and chords.
– Benefits of pre-fabricated timber roof trusses.
– Non-destructive assessment for historic timber trusses.
– Structural load-carrying tests on wooden trusses.
– Influence of historical figures like Palladio and Simona Valeriani on truss design.
A timber roof truss is a structural framework of timbers designed to bridge the space above a room and to provide support for a roof. Trusses usually occur at regular intervals, linked by longitudinal timbers such as purlins. The space between each truss is known as a bay.
Key:1: ridge beam, 2: purlins, 3: common rafters. This is an example of a "double roof" with principal rafters and common rafters.
Rafters have a tendency to flatten under gravity, thrusting outwards on the walls. For larger spans and thinner walls, this can topple the walls. Pairs of opposing rafters were thus initially tied together by a horizontal tie beam, to form coupled rafters. But such roofs were structurally weak, and lacking any longitudinal support, they were prone to racking, a collapse resulting from horizontal movement. Timber roof trusses were a later, medieval development. A roof truss is cross-braced into a stable, rigid unit. Ideally, it balances all of the lateral forces against one another, and thrusts only directly downwards on the supporting walls. In practice, lateral forces may develop; for instance, due to wind, excessive flexibility of the truss, or constructions that do not accommodate small lateral movements of the ends of the truss.
Definition from ChatGPT:
Timber roof truss:
A timber roof truss is a structural framework designed to support the roof of a building. It is typically made of timber beams that are interconnected to form a triangular shape, providing stability and strength to the roof structure. Timber roof trusses are commonly used in residential and commercial construction to create open and spacious interior spaces without the need for interior support walls.