timberComplexBeamITI

Design and analyze timber beams with multiple spans and load cases to AS 1720.1:2010. ITI version with extended capabilities.

## Method & scope | Property | Detail | | -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | What it checks | Structural model, Bending capacity (AS 1720.1:2010, Cl. 3.2), Stability factor k8 and lateral-torsional buckling (Cl. 3.2.5), Shear capacity (AS 1720.1:2010, Cl. 3.2.3), Bearing capacity (AS 1720.1:2010, Cl. 3.2.6), Deflection checks, Load combinations | #### Calculation method The ITI Timber Beam v2 calculator designs timber beams using Limit State Design per AS 1720.1:2010 Amendment 3. It runs a first-order elastic analysis to determine moment, shear, and deflection demands under each load combination, then checks those demands against AS 1720.1 design capacities adjusted for timber species, grade, moisture condition, load duration, and restraint. ##### Structural model The calculator models the beam as a one-dimensional element and computes bending moment, shear force, and deflection diagrams under each load case. Loads are entered by type, permanent (G), imposed (Q), wind (W), and governing ULS and SLS combinations are generated automatically per AS/NZS 1170.0 and AS/NZS 1170.1. For continuous beams with multiple intermediate supports, the moment and shear envelopes are evaluated across all spans simultaneously. ##### Bending capacity (AS 1720.1:2010, Cl. 3.2) The design moment capacity phi × Md is determined from the characteristic bending strength and the relevant capacity modification factors: **phi × Md = phi × k1 × k4 × k6 × k8 × k9 × k12 × f'b × Z** Where: * **phi**, capacity reduction factor (0.85 for bending per AS 1720.1 Table 2.1) * **k1**, load duration factor; ranges from 0.57 for permanent load to 1.0 for short-term imposed or 1.14 for wind * **k4**, partial seasoning factor, applied when member moisture content is between green and seasoned thresholds * **k6**, temperature factor for elevated temperature environments * **k8**, member restraint and stability factor accounting for lateral-torsional buckling of the compression edge (Cl. 3.2.5) * **k9**, factor for strength sharing in multiple-member systems * **k12**, stability factor for combined bending and compression (relevant in beam-column configurations) * **f'b**, characteristic bending strength for the nominated species-grade combination (MPa) * **Z**, section modulus (mm³) The bending utilization check is: *M* / (phi × Md) ≤ 1.0\* ##### Stability factor k8 and lateral-torsional buckling (Cl. 3.2.5) k8 accounts for lateral buckling of the compression edge and governs when the beam is unrestrained over a significant unbraced length. The effective length for minor-axis buckling is derived from the unbraced segment length and the end-restraint conditions. The calculator evaluates k8 automatically from the slenderness parameter S1 or S4 per AS 1720.1 Table 3.2. When full lateral restraint is provided to the compression edge (e.g. by a continuous floor diaphragm bearing on the top face), k8 = 1.0 and no buckling reduction applies. ##### Shear capacity (AS 1720.1:2010, Cl. 3.2.3) The design shear capacity phi × Vd is: **phi × Vd = phi × k1 × k4 × k6 × f's × As** Where f's is the characteristic shear strength and As is the effective shear area (2/3 × b × d for rectangular sections). The shear demand V\* is taken at the critical section, which is located at a distance d (depth) from each support face. The utilization check is: *V* / (phi × Vd) ≤ 1.0\* ##### Bearing capacity (AS 1720.1:2010, Cl. 3.2.6) At each support, bearing stress is checked against the characteristic bearing strength f'p applied over the contact area. Moisture condition and load duration factors are applied consistently with the bending and shear checks. *R* / (phi × Rpd) ≤ 1.0\* ##### Deflection checks Two independent serviceability checks are performed per span: * **Short-term deflection**, instantaneous elastic deflection under imposed or wind loads, checked against a user-defined span/n ratio or an absolute limit in mm * **Long-term deflection**, total deflection including creep under sustained permanent and long-term imposed loads, checked against a separate span/n ratio Deflections are computed from the elastic bending stiffness EI of the cross-section. Load duration factors for the permanent load component follow AS 1720.1 Appendix B creep modification guidelines. ##### Load combinations Strength (ULS) combinations follow AS/NZS 1170.0 Table 4.2 including 1.35G, 1.2G + 1.5Q, 1.2G + 1.5psQ + Ws, and wind-governing combinations. Serviceability (SLS) combinations use 1.0G + 1.0Q and 1.0G + 0.7Q for long-term deflection in line with AS/NZS 1170.1 Appendix C. The governing combination is identified for each check and reported alongside the utilization ratio. ##### Load linking Support reactions are exported as linked outputs. Column calculators placed downstream in the same Calcs.com project, including the ITI Timber Column v1, receive updated reactions automatically whenever beam inputs change. This eliminates manual load transfer between templates and keeps the full load path synchronized when section sizes or loads are revised. ## How to use it Open it from **Run calc** in the About this calculator panel above. Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See [Checks, References, Conditions and Assumptions](/docs/running-calculations/checking-results/checks-references-conditions-assumptions). Check the utilization of each governing check in the summary, then export a PDF report. See [Views and Export](/docs/running-calculations/exporting-reports/views-and-export). ## Common questions AS 1720.1:2010 with Amendment 3 (Timber Structures). The calculator checks bending, shear, and deflection limit states per AS 1720.1, applying the relevant capacity reduction factors and load duration factors for the specified timber species and loading. The underlying design logic is identical to the standard Timber Beam calculator. Key inputs include span configuration (simple, continuous, or cantilever with multiple supports), timber species and strength grade, cross-section dimensions, and applied loads by type (permanent, imposed, wind). ITI-specific presets and section defaults are pre-loaded to match the standard configurations used in ITI's engineering workflow, reducing data entry on routine projects. Bending capacity utilization (M\* / phiMd ≤ 1.0), shear capacity utilization (V\* / phiVd ≤ 1.0), and deflection against the limits in AS 1170.1 and AS 1720.1. Results are displayed as traffic light pass/fail checks for each limit state with clause references. Stability factor k8 is computed automatically based on restraint conditions and effective unbraced length. This is a customized version of the Timber Beam calculator configured for ITI's specific workflow. ITI-standard section defaults, load presets, and project documentation settings are pre-applied so engineers in the ITI account can open common beam configurations without manually re-entering routine values. The underlying AS 1720.1 design logic is identical to the standard Timber Beam calculator. Yes. The calculator supports multiple intermediate supports in a single analysis, automatically computing the moment and shear envelopes across the continuous beam under AS/NZS 1170.1 ULS and SLS load combinations. Span lengths and support conditions are configured individually for each span. Yes, beam support reactions link directly to connected column calculations in the same Calcs.com project. When span lengths, loads, or section sizes change in the beam, the linked column automatically receives the updated reaction forces. No manual re-entry is needed between beam and column templates. ## Next steps Complete list of Calcs.com design calculators available for Australian and New Zealand projects (AS 3600, AS 4100, AS 1720, AS/NZS 1170, and related standards). Design timber beams with multiple spans and load cases to AS 1720.1:2010 (Amdt 3). Checks bending, shear, bearing and deflection. Design timber truss chords, frame members and rafter ties to AS 1720.1:2010 (Amdt 3), with combined bending, axial and shear checks.