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TOPIC OVERVIEW
TOPIC OVERVIEW
This module provides a comprehensive overview of structural systems used in multi-storey timber construction. It introduces the main system typologies, detailing their core components, benefits, and inherent limitations. Furthermore, it analyzes the load-transfer mechanisms specific to each system. Relevant standards and recommended literature for advanced study are also included.
TABLE OF CONTENTS
TABLE OF CONTENTS
INTRODUCTION
INTRODUCTION
Timber buildings can be built using different structural systems. Typically some systems are based on load-bearing walls, while others use frames, made of beams, columns, braces or arches. There are also cases where buildings employ hybrid systems that combine both approaches.
The choice of the structural system affects how the building carries vertical loads, such as self-weight, floors and live loads, and horizontal loads, such as wind and seismic forces.
STRUCTURAL TYPOLOGIES: LOAD-BEARING WALL SYSTEMS
STRUCTURAL TYPOLOGIES: LOAD-BEARING WALL SYSTEMS
CLT buildings
CLT buildings
Cross-Laminated Timber (CLT) buildings are constructed using large mass timber panels for walls, floors, and roofs, connected together to form a rigid three-dimensional structural box. The most common assembly method is the platform configuration, where the vertical walls are interrupted at each storey by the floor elements. This approach is highly efficient, as each completed floor acts as a safe working platform for erecting the subsequent level, ensuring fast erection and high dimensional accuracy.
To optimize structural performance, the panel layers are specifically oriented according to their function. Wall panels typically have their outer layers oriented vertically so that the majority of the lamellas run parallel to the gravitational forces, maximizing compressive strength. Conversely, floor panels have their outer layers oriented parallel to the floor span (usually the longer dimension of the panel) to provide a higher bending moment of inertia.
Schematics adapted from EN 1998-1-2
Despite their cross-laminated structure providing out-of-plane strength and stiffness in both directions, floor panels are predominantly designed and analysed as one-way spanning elements.
In the global structural response, CLT panels provide both load-bearing capacity and lateral stability. Vertical loads are transferred downwards via direct compression through the wall panels. Under horizontal loads (such as wind or seismic actions), the floors act as rigid diaphragms, distributing forces to the shear walls. These walls rely on their in-plane stiffness to resist the actions and transfer them to the foundations. Because forces are transferred discretely at panel boundaries, mechanical connections are critical design aspects..
Key elements to observe:
Hold-downs: resist uplift forces at wall ends caused by overturning.
Shear brackets: transfer horizontal shear forces at the base of the wall.
Panel-to-panel connections: ensure continuity between adjacent wall and floor elements.
Perpendicular-to-grain compression: requires careful checking in medium-to-high-rise buildings to prevent the crushing of floor panels sandwiched between vertical walls.
Light Timber Frame (LTF) buildings
Light Timber Frame (LTF) buildings
Light timber frame construction is based on a regular grid of closely spaced, slender timber elements. Walls and floors are built from small-section timber studs and horizontal rails (typically 60–100 mm × 120–240 mm), which are braced with structural wood-based sheathing panels (usually 12–15 mm thick). This system is lightweight, highly modular, and particularly suitable for prefabricated wall, floor, and roof elements.
The structural efficiency of this system relies on the principle of diffuse load distribution. Rather than concentrating loads on a few heavy columns, vertical loads from the roof and floors are shared across a large number of lightly loaded vertical studs that transfer the forces to the ground. Lateral stability is achieved through the composite action of the timber frame, the sheathing panels, and the mechanical fasteners acting as shear wall.
Based on the continuity of the vertical elements, two main frame typologies exist:
Platform Frame: Vertical studs are interrupted at each floor level. The floor decks rest on the walls below, acting as working platforms, and construction proceeds storey by storey.
Balloon Frame: Vertical studs extend continuously for the full height of the building, and the floor decks are hung or connected directly to the inner face of the continuous walls
Schematics adapted from EN 1998-1-2
Because the light-frame system relies on a continuous and regular grid, introducing architectural openings (doors and windows) interrupts the natural descent of loads to the ground. Managing these interruptions requires specific structural detailing to prevent unwanted load concentrations.
Key design aspects for openings:
Headers and Doubled Studs: Structural wooden headers (lintels) must be installed above openings to bridge the gap. These elements safely transfer the interrupted vertical loads to doubled or reinforced studs located at the edges of the opening.
Aligned Openings: The system achieves its maximum economic and structural efficiency when architectural openings are strictly aligned vertically across floors. This alignment preserves the regular flow of forces down to the foundations.
Non-Aligned Openings: Disrupting the regularity of the frame with offset openings causes loads to concentrate at specific points. This requires the insertion of heavy transfer beams, a solution that directly contradicts the core philosophy of light-frame construction based on uniform, diffuse load distribution.
Log-house buildings
Log-house buildings
Log-house buildings are formed by horizontal timber logs or beams stacked one above the other to create continuous load-bearing walls. The structural system is based on the direct contact between the timber elements, combined with interlocking corner joints, grooves and vertical connectors. Vertical loads are transferred through the stacked walls, while horizontal stability depends on the interaction between logs, friction, corner detailing and anchorage. Compared with panel-based systems, log-house construction has a more layered behaviour and can be sensitive to settlement, shrinkage and moisture-related movements.
Schematics adapted from EN 1998-1-2
The example shows a wall made of stacked timber elements. Each log or beam contributes to the vertical load path, while the contact between elements helps transfer compression forces. The corners are particularly important because they provide geometric interlocking and help stabilise the wall in the horizontal direction.
Important aspects to observe:
Stacked logs: transfer vertical loads through direct compression.
Corner joints: provide interlocking and lateral stability.
Vertical connectors: limit relative sliding and improve wall continuity.
Settlements: must be considered because timber elements can shrink or compress over time.
Timber-framed walls with masonry infill
Timber-framed walls with masonry infill
Timber-framed walls with masonry infill combine a structural timber skeleton with interstitial materials. Rather than solid panels, these infills typically consist of heterogeneous or relatively incoherent elements like rubble stone, earth, or loose bricks, as seen in traditional practices such as Hımış in Turkey or Dhajji Dewari in the Indian subcontinent.
The structural behaviour of these hybrid systems is highly complex. Defying the simplistic model where the timber frame strictly carries vertical loads and the masonry solely provides lateral stiffness, the reality is far more interactive: timber diagonals actively contribute to lateral resistance, while the infill often participates in transferring vertical forces. This category encompasses numerous regional variations historically developed as highly effective earthquake-resistant systems, including the Gaiola Pombalina in Portugal, the Casa Baraccata in Italy, and the traditional frames of Lefkas in Greece.
Although rarely adopted for modern constructions, this typology holds immense heritage value. Comprehending the nuanced interactions between the timber members and the diverse infill interfaces remains crucial for the structural assessment, conservation, and seismic retrofitting of existing historic buildings.
Schematics adapted from EN 1998-1-2
The example shows traditional buildings where timber framing and masonry infill work together. The timber members form the visible structural grid, while the masonry fills the spaces between them. Under horizontal actions, the infill can stiffen the wall and modify the distribution of forces within the frame.
Important aspects to observe:
Timber frame: typically carries loads and defines the structural grid.
Infill material: contributes to lateral stiffness and vertical load transfer, though it may introduce local damage mechanisms.
Interfaces: contact conditions and friction between the timber and the infill strictly govern the global structural response.
Diagonal members: resist lateral loads in compression alongside the infill, as traditional mortise-and-tenon joints transfer forces primarily through direct contact.
Timber-framed walls
Timber-framed walls
Timber-framed walls are structural systems composed of regularly spaced vertical posts, horizontal beams, and diagonal timber braces, typically connected through traditional carpentry joints (e.g., mortise and tenon).
The lateral behaviour of these systems is primarily governed by the arrangement of the diagonal members and the mechanical response of the joints. In many traditional configurations, carpentry joints are significantly more effective in compression than in tension. This characteristic makes the overall structural response highly sensitive to load direction, joint detailing, and potential force reversals. Additionally, sarking and timber board overlays can contribute to the lateral stability of the building, depending on their orientation and specific connection details.
This typology encompasses a wide range of traditional structures developed across various regions, often relying on unique local construction techniques. Although less common in modern engineering practice, timber-framed walls remain highly relevant for the assessment, conservation, and strengthening of historic buildings, where understanding the precise role of braces, joints, and member continuity is essential.
Schematics adapted from EN 1998-1-2
The image on the right shows a notable example of a traditional timber-framed building: the Old Government Buildings in Wellington, New Zealand. Completed in 1876, it stood as the world’s second-largest wooden building until 1998.
Important aspects to observe:
Timber frame: Carries vertical loads and defines the main structural grid.
Diagonal members: Provide lateral stability via triangulation, often supplemented by sarking and board overlays.
Carpentry joints: Transfer forces primarily through direct contact, bearing, and compression.
Load direction: Dictates the structural response, as traditional joints and braces perform significantly better in compression.
Member continuity: Governs force redistribution and influences stability under horizontal actions.
STRUCTURAL TYPOLOGIES: FRAME SYSTEMS
STRUCTURAL TYPOLOGIES: FRAME SYSTEMS
Moment-resisting timber frames
Moment-resisting timber frames
Moment-resisting timber frames are composed of beams and columns connected by rigid or semi-rigid joints. Unlike braced systems, they do not rely on diagonal members or shear walls to provide lateral stability. Instead, horizontal loads are resisted through the bending of beams and columns and through moment transfer at the structural joints. Architecturally, this system allows for flexible layouts, large unobstructed openings, and open façades. Structurally, however, it requires meticulously designed connections. In timber construction, the semi-rigid stiffness and yielding strength of these joints typically govern the global behaviour of the frame. Consequently, the cross-sectional dimensions of the timber members are frequently dictated not by internal stresses, but by the geometric necessity to accommodate the mechanical fasteners while complying with code-mandated minimum spacings and edge distances.
The examples highlight the importance of beam-column joints. In a moment-resisting frame, the connection is not just a support detail: it must transfer bending moments, shear forces and axial forces between members. Steel plates, bolts, dowels, screws or concealed connectors are often used to achieve the required stiffness.
Key elements to observe:
Beam-column joints: provide rotational stiffness and moment transfer.
Column bases: transfer bending and shear forces to the foundation.
Open bays: possible because no diagonal bracing is required.
Connection detailing: critical for deformation control and lateral resistance.
Schematics adapted from EN 1998-1-2
Braced timber frames
Braced timber frames
Braced timber frames use beams and columns to carry vertical loads, while diagonal braces resist horizontal actions. The diagonal members transform the frame into a triangulated system, making it much stiffer against lateral displacement. Horizontal forces are mainly transferred through axial tension and/or compression in the braces. This system is structurally efficient because axial forces are generally easier to resist than bending moments. The main design aspects are the bracing layout, the slenderness of compression members and the detailing of brace-to-frame connections.
Schematics adapted from EN 1998-1-2
The example should be read by following the diagonal members. When a horizontal action is applied, the braces create a direct force path towards the supports and foundations. Depending on the configuration, one diagonal may work mainly in tension while another may work in compression.
Image courtesy of Rubner Holzbau Srl
Important aspects to observe:
Diagonal braces: carry horizontal loads through axial forces.
Brace connections: must transfer forces without excessive slip.
Triangulation: prevents the frame from deforming as a mechanism.
Compression braces: require buckling checks, especially for slender timber members.
Arches, portals and domes
Arches, portals and domes
Arches, portals and domes are geometry-driven structural systems. Their efficiency comes from their shape, which allows loads to be transferred through a combination of axial forces, bending moments and support reactions. They are commonly used for long spans, roofs and large open spaces where intermediate supports are not desirable. In timber construction, these systems are often made from glulam because curved, tapered and large-section members can be manufactured with high precision. Stability out of the main structural plane is a key design issue.
Schematics adapted from EN 1998-1-2
The example shows how geometry can be used to carry loads efficiently over a large span. Curved or portal-shaped members redirect roof loads towards the supports, reducing the need for internal columns. However, these systems must also be stabilised out of plane.
Image courtesy of Rubner Holzbau Srl
Important aspects to observe:
Curved or portal geometry: governs the main load path.
Supports: may receive significant horizontal reactions.
Rigid or hinged joints: strongly influence internal forces.
Lateral bracing and purlins: prevent out-of-plane instability of the main members.
Truss systems
Truss systems
Truss systems are made of timber members arranged in triangular configurations. The triangular geometry allows loads to be transferred mainly through axial tension and compression, reducing bending in the individual members. This makes trusses efficient for roofs, halls and long-span structures. The structural behaviour depends on the arrangement of the members, the support conditions and the design of the nodes. Although trusses are often idealised as pin-jointed systems, real connections may introduce eccentricities, slip and partial rotational stiffness.
Schematics adapted from EN 1998-1-2
The example should be read by looking at the triangulated load path. Loads are distributed through a network of timber members, with some elements working in compression and others in tension. The nodes are the most important details because they collect and transfer forces from several members at the same point.
Key elements to observe:
Triangular geometry: provides stiffness and structural efficiency.
Compression members: require buckling and lateral stability checks.
Tension members: depend strongly on connection capacity.
Nodes and plates: transfer axial forces between members.
Global bracing: needed to stabilise the truss out of plane.
STRUCTURAL RESPONSE: VERTICAL LOADS
STRUCTURAL RESPONSE: VERTICAL LOADS
The timber structural typologies presented above differ in terms of geometry, materials, connections and construction method. However, when looking at how loads are transferred through the building, they can be simplified into two main structural schemes: frame systems and load-bearing wall systems.
In frame systems, loads are mainly collected by beams and transferred to columns, creating a more concentrated load path. In load-bearing wall systems, loads are transferred through continuous wall elements, creating a more distributed load path.
Response schematization
Response schematization
Frames
In frame systems, vertical loads are collected by floors or roof beams and transferred to columns. The load path is concentrated at beam-column joints and column bases, which usually leads to higher local forces in the foundations.
Load-bearing walls
In load-bearing wall systems, vertical loads are transferred through walls. The load path is more distributed than in frame systems, reducing force concentration but requiring good vertical alignment of walls between storeys.
Preliminary sizing
Preliminary sizing
Below is a selection of sizing tables from manufacturers and literature for the most widely used engineered timber products. This non-exhaustive list is provided to help readers identify preliminary member geometries and cross-sections.
Solid wood:
Binderholz. (2024). Solid Wood for Construction KVH. https://www.binderholz.com/fileadmin/user_upload/pdf/products/solid_wood_for_construction_kvh.pdf
HASSLACHER group. (n.d). Structural finger jointed solid timber. https://www.hasslacher.com/data/_dateimanager/broschuere/HNT-Konstruktionsvollholz-EN.pdf
Glulam:
Binderholz. (2024). Glulam GLT. https://www.binderholz.com/fileadmin/user_upload/pdf/products/glulam.pdf
HASSLACHER group. (n.d). Glued Laminated Timber. https://www.hasslacher.com/data/_dateimanager/broschuere/HNT-Brettschichtholz-EN.pdf
Swedish Wood. (2024). The Glulam Handbook Volume 1 (pages 46-51) https://www.swedishwood.com/siteassets/5-publikationer/pdfer/glulamhandbook1-240508.pdf
Cross-Laminated Timber (CLT):
Binderholz. (2024). CLT BBS. https://www.binderholz.com/fileadmin/user_upload/pdf/products/clt_bbs.pdf
KLH Massivholz GmbH. (2024). Structural pre-analysis tables. https://www.klh.at/wp-content/uploads/2019/09/klh-structural-pre-analysis-tables.pdf
HASSLACHER group. (n.d). Cross laminated timber. https://www.hasslacher.com/data/_dateimanager/broschuere/HNT-Brettsperrholz-EN.pdf
Swedish Wood. (2019). The CLT Handbook. (pages 27-29) https://www.swedishwood.com/siteassets/5-publikationer/pdfer/clt-handbook-2019-eng-m-svensk-standard-2019-2022.pdf
Safety checks
Safety checks
For details on the design and verification of beams, columns, and connections, you can refer to the following pages of this site:
Timber elements and their design
Connections, beam supports and reinforcements
Extensive detailed information on the structural verification of timber elements can be found in open-access publications available online, such as the "Design of timber structures" book series by Swedish Wood at https://www.swedishwood.com/
Swedish Wood. (2022). Design of timber structures Volume 1 edition 3 https://www.swedishwood.com/siteassets/5-publikationer/pdfer/sw-design-of-timber-structures-vol1-2022.pdf
Swedish Wood. (2022). Design of timber structures Volume 2 edition 3 https://www.swedishwood.com/siteassets/5-publikationer/pdfer/sw-design-of-timber-structures-vol2-2022.pdf
Swedish Wood. (2022). Design of timber structures Volume 3 edition 3 https://www.swedishwood.com/siteassets/5-publikationer/pdfer/sw-design-of-timber-structures-vol3-2022.pdf
Given the widespread use of CLT and LTF technologies in multi-storey buildings, the fundamental structural aspects to verify under vertical loading are summarized below.
CLT structures
Stability verification of the wall
Combined axial load and bending check, typically including out-of-plane wind action.
Verification of the floor
Checks include bending, shear, rolling shear, deflection, vibration, and compression perpendicular to the grain at the support zones.
Verification of the lintel
Modeled as a simply supported or fixed-end beam, depending on the specific construction details.
LTF structures
A. Studs (out-of-plane buckling). Verify for out-of-plane instability, assuming that in-plane longitudinal buckling is prevented by the sheathing panels nailed to the studs. For perimeter walls, horizontal wind loads must be considered, and the verification must account for combined bending and axial compression;
B. Top plate. To be verified as a continuous beam on multiple supports;
C. Lintel. Modeled as a simply supported beam. Serviceability Limit State (SLS) deformability checks are crucial here to ensure the correct functioning of the openings (doors and windows).
D.E. Bottom plate (compression perpendicular to the grain). Compression perpendicular to the grain must be checked at the stud-to-plate interface. Attention should be paid to edge/corner studs (D), where the effective bearing area is minimized, and internal studs (E), where the applied compressive load might be maximal.
STRUCTURAL RESPONSE: HORIZONTAL LOADS
STRUCTURAL RESPONSE: HORIZONTAL LOADS
Response schematization
Response schematization
Moment-resisting frames
Moment-resisting frames transfer horizontal forces through bending in beams and columns. The key design aspect is the rotational stiffness and strength of the semi-rigid beam-column joints.
Braced frames
Frames with pinned connections lack inherent lateral stability and must rely on additional vertical stabilising systems, such as diagonal bracing, shear walls, or cores. These vertical elements work in combination with floor and roof diaphragms to establish a continuous and effective load path, transferring horizontal forces safely down to the foundations.
Load-bearing walls
Wall systems resist horizontal actions through in-plane shear and rocking of the walls. Hold-downs, shear brackets and floor-to-wall connections are essential to transfer forces safely to the foundations.
Bracing systems
Bracing systems
Bracing systems are fundamental for the stability of timber buildings, serving a dual purpose. They not only resist external horizontal actions, such as wind and earthquakes, but also prevent global instability phenomena caused by unavoidable geometric imperfections under purely vertical loads. By providing essential stiffness, lateral resistance, and a continuous load path to the foundations, bracing systems transform a theoretically unstable frame into a highly robust and secure structure.
In heavy timber structures, overall stability depends on the correct arrangement of bracing systems in three dimensions. Horizontal actions are not resisted by a single element, but by a combination of vertical and horizontal bracing systems working together.
Schematics adapted from The Glulam Handbook - Volume 2 (Figure 13.5) - Sweedish Wood
To identify the different bracing elements, it is useful to consider both their position in the structure and their direction of action. Some bracing elements are placed in vertical planes, such as longitudinal walls or end walls. Others are arranged in horizontal or inclined planes, such as roof or floor diaphragms.
(A) Longitudinal wall bracing
(B) Transversal roof bracing
(C) End wall bracing
(D) Longitudinal roof bracing
Wall bracing systems
Wall bracing systems
A timber frame consisting solely of beams and columns may be capable of carrying vertical loads, but it is not inherently stable under horizontal actions. In the absence of an adequate lateral load-resisting system, the frame can undergo rigid-body lateral displacement, behaving kinematically as a mechanism (Fig. a).
It should be noted that, even under purely vertical loading, a frame lacking any lateral restraint is theoretically stable only under the idealised assumption of perfect geometry. In practice, unavoidable imperfections (such as out-of-plumb columns, load eccentricities, or initial curvature of members) introduce second-order effects that can amplify lateral displacements and potentially lead to instability. This is the physical basis of the notional horizontal load concept adopted in structural design codes, which accounts for geometric imperfections by means of an equivalent horizontal force applied to the otherwise perfectly vertical structure.
Lateral stability can be achieved through different strategies: by introducing diagonal bracing members, by incorporating rigid shear panels or diaphragms, by providing moment-resistant connections at the beam-column joints, or by fixing the base of the vertical elements to the foundation. Each solution relies on a distinct load path, but the underlying objective is the same: to prevent excessive lateral drift and to ensure the safe transfer of horizontal forces to the foundations (Fig. b–e).
Unstable configuration
Schematics taken from The Glulam Handbook - Volume 2 (Figure 13.1) - Sweedish Wood
Stable configuration
Diagonal bracing: introducing diagonal members to create a truss (b).
Shear walls: incorporating shear panels or diaphragms (c).
Moment-resisting frames: providing moment-resistant connections at the beam-column joints (d).
Cantilever columns: fixing the base of the vertical elements to the foundation (e).
3D Stability and Load Path Continuity
3D Stability and Load Path Continuity
The stability of a timber structure must always be considered in three dimensions. Bracing elements are typically arranged both in vertical planes (such as walls and frames) and in horizontal or inclined planes (such as floors and roofs). The core design principle is straightforward: horizontal forces must always have a continuous and well-defined load path to the ground.
The main 3D schematic illustrates this continuity, showing how lateral forces acting on the building envelope are collected by the longitudinal roof bracing and safely transferred to the vertical bracing systems located at the ends of the building.
When designing the lateral load-resisting system for a multi-bay building, engineers can adopt different strategies, which lead to distinct global behaviours:
End-braced systems (Fig. a): In this configuration, intermediate frames are pin-jointed (laterally unstable on their own) and "lean" on the horizontal roof truss for support. The roof bracing acts as a deep horizontal beam transferring the lateral loads to the vertical end walls. Because the roof truss itself is flexible and deforms under load, the central frames will undergo significantly larger lateral displacements compared to the frames closer to the stiff end walls. This differential drift can become a critical design issue in very long structures.
Moment-resisting frames (Fig. b): Alternatively, lateral stability can be distributed throughout the structure. By utilizing rigid, moment-resisting connections at the beam-column joints, every single frame becomes self-sufficient in resisting lateral loads. This solution relies on shorter, more direct load paths to the foundations, resulting in a much more uniform lateral deformation profile along the entire length of the building.
Schematics adapted from The Glulam Handbook - Volume 2 (Figure 13.1) - Swedish Wood
The examples show how bracing systems are integrated into real timber structures. Diagonal members, roof bracing and secondary elements are used not only to resist wind or seismic actions, but also to stabilise the main structural members against out-of-plane movement.
In practice, bracing is not a secondary detail. It controls the global stability of the structure, reduces lateral displacements and prevents local instability of beams, columns or frames. For this reason, the position, continuity and connection detailing of bracing elements are essential parts of the structural design.
Image courtesy of of Rubner Holzbau Srl
Roof and floor bracing systems
Roof and floor bracing systems
Roof and floor bracing systems collect horizontal actions acting on the building envelope and transfer them to the vertical resisting elements. For the system to function efficiently, the roof or floor plane must not behave as a set of independent beams, but rather as a fully interconnected structural unit capable of distributing forces.
As illustrated in the figures, the internal forces developed within the transfer members depend on the direction of the external horizontal actions. Taking wind pressure and suction as an example, when the direction of the external action changes, the internal forces within the structural elements undergo a complete load reversal. Consequently, a longitudinal member acting as a tie in tension (T) under one load case (Fig. a) will act as a strut in compression (C) when the load direction is reversed (Fig. b). This alternating structural behaviour can become a critical design aspect. Therefore, in building configurations such as that in the figure, both the timber elements and, most importantly, their mechanical connections must be carefully designed to safely transfer both tensile and compressive forces.
Schematics taken from The Glulam Handbook - Volume 2 (Figure 13.23) - Swedish Wood
Roof bracing can be arranged in various configurations depending on the span, building geometry, and the overall structural system. As illustrated in the schematics, common solutions include steel cross bracing with tension rods (Fig. a), V-shaped timber diagonals (Fig. b), and K-shaped timber bracing layouts (Fig. c).
The choice of material and geometry is heavily influenced by the expected structural behaviour. Steel rods are highly efficient for bracing members acting primarily in tension. Conversely, timber diagonals are preferred when fire performance, architectural integration, or compression resistance are required. To optimize compression capacity, geometries like the K-shape are often adopted specifically to reduce the effective buckling length of the diagonals. Ultimately, the chosen layout dictates the roof's in-plane stiffness, the internal force distribution, and the complexity of the connection design.
A roof or floor can also function as a structural diaphragm. In this configuration, horizontal forces are transferred through panels, boards, or sheathing elements adequately connected to the supporting timber members. The diaphragm effectively acts as a deep horizontal beam, collecting lateral forces and delivering them to the vertical bracing systems. This mechanism requires continuous connections between panels, edge members, and supporting beams, as openings or discontinuities can severely interrupt the load path.
The internal force distribution within the diaphragm depends heavily on the global bracing strategy:
End-braced systems (Fig. a): The diaphragm acts as a deep, simply supported beam spanning between the end shear walls, which absorb the entirety of the transverse loads. Because the in-plane shear forces are maximum at the supports and approach zero at mid-span, the panel-to-panel shear connections can often be optimized and reduced in the central region of the roof.
Shared-resistance systems (Fig. b): When intermediate moment-resisting frames are present, they provide additional lateral stiffness, acting like elastic springs. The horizontal load is therefore shared between the diaphragm and the frames. In this "frame + diaphragm" interaction, the internal forces within the diaphragm are governed by the relative stiffness of the respective components, requiring a specific calculation to accurately assess the load distribution.
Schematics modified and adapted from The Glulam Handbook - Volume 2 (Figure 13.27) - Swedish Wood
The examples show roof bracing systems integrated into real timber structures. Diagonal members and roof-plane bracing connect the main beams and prevent the structure from deforming laterally. These elements also help stabilise slender beams against out-of-plane movement.
In practice, roof bracing has two roles: it transfers horizontal actions to the vertical bracing systems and stabilises the main structural members. For this reason, its position, continuity and connection detailing are essential for the global stability of the building.
Images from Piazza M., Tomasi R., Modena R., "Strutture in legno" (Hoepli 2005)
Safety checks
Safety checks
Due to the widespread adoption of CLT and LTF systems in multi-storey construction, the primary structural verifications concerning horizontal loads are outlined below.
For CLT structures: verification for in-plane horizontal loads on walls (wind and seismic action)
Check the possible mechanisms of:
A. In-plane failure of the timber panel;
B. Rigid-body translation (sliding) of the floors;
C. Rigid-body translation of the walls (verification of shear brackets);
D. Rigid-body rotation of the walls (verification of hold-down anchors).
For LTF structures: shear capacity of the light frame timber wall
Under horizontal loading, it is necessary to:
Verify the shear resistance of panel-to-frame connections using Johansen theory (i.e., European Yield Model);
Verify the studs for tension and compression;
Verify the bottom rail for compression perpendicular to the grain;
Verify the sheathing panel for in-plane shear.
Rigid translation of the floors
Floor-panels must be adequately connected to the wall-panels.
Rigid translation & rotation of the walls
Rigid translation and rotation of the walls must be prevented by installing appropriate anchoring devices (e.g., shear brackets and hold-downs).
📄 ASSIGNMENT
📄 ASSIGNMENT
Overview and aim
Overview and aim
The aim of this assignment is to design a multi-storey timber structure.
The assignment is structured into different tasks that range from the overall design to detailed verifications; as such, it can be taken partially depending on specific needs. To fully complete the assignment, a clear understanding of topics such as Materials – timber, mass-timber and engineered wood products, Timber Elements and their design, and Connections, beam supports and reinforcements is required.
Requirements
Requirements
Students undertaking this assignment should possess:
Statics: understanding of equilibrium, internal forces, and structural behavior.
Technical Architecture: ability to define suitable construction packages.
Structural Mechanics & Building Technology: basic knowledge of materials and construction techniques.
Earthquake Engineering: introductory concepts in seismic design.
Timber Construction: familiarity with engineered wood products and timber structural elements.
These prerequisites ensure students can effectively tackle the assignment’s design and analysis tasks.
Learning outcomes
Learning outcomes
By completing this assignment, students will be able to:
Select the optimal construction technology and identify the structural layout
Size structural elements and connections.
Verify structural performance under vertical and horizontal loads.
A downloadable file has been created for this assignment, which instructors and tutors can distribute to students. The file can be modified and updated according to assigned parameters and group specifications, offering practical support for the design of the timber structure.
Assignment Structural systems.pdfREFERENCES
REFERENCES
Further references:
structural verification of CLT components under gravitational forces and lateral loading:
Swedish Wood. (2019). The CLT Handbook. https://www.swedishwood.com/siteassets/5-publikationer/pdfer/clt-handbook-2019-eng-m-svensk-standard-2019.pdf
FPInnovations. (2019). Canadian CLT Handbook - Volume I. https://web.fpinnovations.ca/wp-content/uploads/clt-handbook-complete-version-en-low.pdf
proHolz Austria. (2018). Cross-Laminated Timber Structural Design Volume 2. https://www.proholz.at/publikationen/cross-laminated-timber-structural-design-volume-ii
EN 1995-1-1:2025 (Clause 3, Annex C.3, Annexes H.3 and H.4)
EN 1998-1-2:2025 (Clause 13)
Stora Enso. (2016). Building Systems by Stora Enso | Residential multi-storey buildings. https://www.cltsk.info/wp-content/uploads/2019/12/Residential-Multistorey-Buildings-Design-Manualfinal-20160620version-14EN_compressed.pdf
Think Wood. (2022). Mass Timber Design Manual. (Available upon request). https://info.thinkwood.com/download/2022-mass-timber-design-manual
Waugh Thistleton Architects. (2018). 100 UK CLT Projects. https://waughthistleton.com/100-projects-uk-clt/
WoodWorks – Wood Products Council. Mass Timber Technical Reference Guide: technical resource hub for mass timber design (structural, fire, acoustics, durability, etc). (manuals available upon request) https://www.woodworks.org/mass-timber-technical-reference-guide/
proHolz Austria. (2018). Cross-Laminated Timber Structural Design Volume 2. https://www.proholz.at/fileadmin/proholz/media/shop_Publikationen/Information_pdf/cross_laminated_timber.pdf
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