Engineered roof trusses are significantly more material-efficient, economical, and effective than traditional carpentry solutions. A key advancement is the use of laminated glued timber (GLULAM) products and composite trusses assembled from varying cross-sections and special profiles, typically bonded or mechanically-fastened together. Another fundamental aspect of their efficiency is precision engineering where every component dimension and connection is determined through detailed structural calculations, ensuring that each element is custom-designed. Connections in engineered roof trusses are made using bolts or specially-engineered connectors, avoiding traditional joinery methods that could compromise structural capacity.
The characteristic connections of engineered carpentry structures and roof trusses are as follows:
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Bolted joints are used to lengthen joints that act as compressed or tensioned beams, and to connect different elements with spliced joints. In these cases, the bolt shanks and walls provide the load-transferring surfaces. Stud bolts are fixed with washers and nuts.
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Wood-insert joints are typically used to splice compressed or tensioned beams. The load transfer is carried across evenly-spaced or single hardwood inserts. The elements are clamped together with stud bolts.
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In metal-insert joints, the hardwood inserts are replaced by split ring, shear or tooth plate connectors, or other steel profile inserts.
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Nailed connections are generally used for fastening boards or planks. Similar to bolts, they can be arranged in varied arrangements and multiple rows.
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Nail plate connectors can connect elements in the same plane with equal thickness. They are generally applied on both sides, allowing multiple elements to be joined.
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Two-way and three-way connectors are precision-formed metal elements designed to accommodate specific timber profiles and joining angles. . Perpendicular connections can be made with joist hangers, brackets, angle brackets, or base plates. These multi-connectors can also be used for splicing or for anchoring inclined members (e.g., rafters). Nails, wood screws, or stud bolts can be used with these connectors.
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Where necessary, glued joints can be used on site toallow for situations such as increasing the height of beams or splicing with fishplates. Such connections can be further reinforced by combining them with other methods (e.g., inserted plate or ring connectors or stud bolts).
1. Engineered roof trusses
Engineered frames or trusses use two types of arrangements:
a) Sparsely-spaced arrangement: engineered structures (for example, timber trusses) are positioned along the principal axes at intervals of every 3–5 rafter spacings. Purlins serve two functions: longitudinal bracing and rafter support.
The truss in the example is made of planks connected with splice plates with the following joints:
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The truss joints are formed with stud bolts and timber spacer blocks clamping the planks together.
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The assembled trusses are secured to the ring beam and the top plate using two-way connectors.
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The additional purlins connect to the trusses with stud bolts or angle brackets.
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The rafters are fixed similarly.
b) Densely-spaced arrangement: the timber frames or trusses form the complete rafter structure. For this purpose, they are placed at rafter-spacing intervals, with 90–140 centimetres bays. Wind bracing is provided by fixing bands fastened in the form of an Andrew’s cross. If required, the end bays can be further stiffened with wind trusses. Typical connections are shown in this example:
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The wall plates are anchored to the building’s ring beam (or floor structure) using anchor studs.
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Trusses or frames are secured with restraining steel brackets (angle brackets). Self-tapping screws are used for fastening the members.
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At the truss joints, the struts are connected with nail plates placed symmetrically on both sides.
c) Engineered roof trusses supported by purlins: The robust solid timber trusses, typically bearing on gable walls, are erected at the purlin positions as in traditional purlin roof construction. Rafters are then laid across these purlins. The series of rafter pairs is hung on the purlins with rafter ties. The ends of the rafter ties are fastened to the rafters with stud bolts. The rafters are further secured to the purlins using structural wood screws or angle brackets.
2. GLULAM Timber Halls
Modern engineered timber structures are ideal for constructing complete halls that meet today’s requirements. These buildings can be used for many purposes, from industrial and agricultural functions to public buildings for sports or cultural activities and are commonly built from glued laminated timber (glulam) beams. The advantage of these is that they do not crack or warp, but have a huge load-bearing capacity, allowing spans of up to 60-70 meters to be achieved. Another benefit of these trusses is that they can be manufactured with variable cross-sections or in curved shapes.
In our example, we present a timber hall whose frames consist of two columns connected by a beam with a variable cross-section. The frame columns are fixed to the base plate with welded steel shoes with anchor plates. The connection between the single column and the beam is designed as a pinned joint, using internal insert plates and bolts In contrast, the connection of doubled, variable cross-section columns to beams forms rigid corner joints with cylindrically-shaped steel insert plates arranged in a circular pattern. The purlins are fixed between the frames with concealed steel shoes. For lateral stability, , steel bracingin the shape of an Andrew’s cross on both the side wall and the roof slab is typically done in the second bay from each gable end. Additional smaller cross-section beams are attached to the finished structure, to which we connect the facade panels.
3. Steel trusses and halls
All structural types built from engineered timber trusses can also be constructed from steel. Steel engineered trusses and joints are also supported by structural calculations. The advantages of steel structures compared to timber ones are their higher load-bearing capacity and achievable stiffness; however, the need for corrosion protection makes their construction and maintenance more complex. Another challenge for steel structures is their much higher susceptibility to thermal expansion. Steel trusses can be produced with a variety of sections, such as:
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Cold-formed steel sections (CFS), C, Z, U sections or hollow sections
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hot-rolled I, H, U, C sections or hollow sections
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unified sections
Connections in steel structures are either permanent welded joints, or detachable bolted assemblies. Steel truss members are typically connected using gusset plates and bolts.
Steel halls are often constructed from welded rigid frames whose joints are further reinforced with stiffeners as well as eave and apex haunches. Columns and beams are most commonly made of I- or H-sections. The columns are bolted to the concrete subfloor via welded base plates. The most common purlin profiles are Z- and C-sections, which are fastened to the rigid frames by bolts. Bolted connections are used to secure the rails that carry the facade panels, as well as the diagonal structural bracings that provide resistance against wind forces.
