RKALC Structural Engineering

WindKALC Advanced

From preliminary building properties to wind response

The example is built around a square, slender office tower and follows both ultimate and serviceability wind assessments, including along-wind and cross-wind response.

Sample RKALC structure

The worked example introduces an office building with a 27 m x 27 m floor plate, a central 9 m x 9 m core, 46 storeys and a total height of 150 m from footings to roof. The resulting aspect ratio is approximately 5.6, so the building is treated as slender.

The objective is not only to estimate wind loads, but also to consider the building response: stiffness, natural period, along-wind and cross-wind actions, drift and occupant acceleration.

What the example covers

Preliminary gravity loads and participating mass.
Core stiffness, roof displacement and a simplified outrigger stiffness check.
Separate ULS and SLS building-period estimates.
Wind region, terrain, damping and directional input setup.
Along-wind and cross-wind base shear and overturning response.
Occupant acceleration and comfort assessment at SLS.
Equivalent static wind-load distributions for export to Excel / ETABS.

WindKALC Advanced worked example showing a 150 metre tall, 27 metre square office building and directional wind response graphs — Worked example overview: 150 m tall, 27 m x 27 m floor plate, central core and along-wind / cross-wind response directions.

Engineering workflow

Worked-example sequence

Move directly to the main stages of the preliminary wind assessment.

Video walkthrough

WindKALC Advanced preliminary wind assessment

Watch the accompanying walkthrough, then use the worked example below to follow the calculations, response checks and equivalent static wind-load workflow in more detail.

Follow the example on screen

The video provides a practical overview of the WindKALC Advanced workflow for the 150 m slender office-building example used throughout this Learning Centre page.

Along-wind and cross-wind response.
ULS and SLS wind assessment.
Building periods and dynamic response.
Occupant acceleration and comfort.
Equivalent static wind loads for structural analysis.

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01 · Building properties

Establish gravity loading, participating mass and core geometry

The preliminary model starts with simple floor loading and an approximate central-core stiffness.

The example adopts a 240 mm post-tensioned slab, taken as 6 kPa, together with 2 kPa superimposed dead load and 3 kPa live load. This produces a stated ULS gravity intensity of 14.1 kPa and an SLS gravity intensity of 11 kPa.

For dynamic properties, the example uses 2 + 6 + 0.3 x 3 = approximately 9 kPa as the participating mass intensity. With the 27 m x 27 m floor plate and a 1.30 allowance for vertical elements, the stated average storey mass is approximately 852,930 kg.

Floor plate 27 m x 27 m

Central core 9 m x 9 m

Height 150 m

Aspect ratio ~ 5.6

ULS gravity load 14.1 kPa

Participating mass load ~ 9 kPa

Worked example page describing floor loads, participating mass, central core dimensions and preliminary core stiffness — Building description, preliminary floor loads, participating mass and simplified core-stiffness calculation.

02 · Preliminary dynamics

Use displacement and effective stiffness to estimate the building period

The example uses simplified cantilever calculations and an outrigger stiffness improvement before estimating separate ULS and SLS periods.

Using an equivalent uniformly distributed lateral wind load of 75 kN/m, the worksheet obtains an elastic roof displacement of approximately 608 mm for the gross core. With a 0.6 effective inertia at ULS, the example displacement becomes about 1,013 mm, approximately H/150.

For serviceability, the worksheet first estimates approximately 494 mm, about H/300, and then adopts a target total SLS building drift of H/400, corresponding to 375 mm at the roof. A simplified outrigger study reduces the elastic displacement to approximately 364 mm.

The worksheet then uses an equivalent global inertia of about 397 m⁴ in the period calculation. With different effective-section factors, the period tool gives approximately 6.94 s at ULS and 6.26 s at SLS in the example.

Gross core inertia ~ 238 m⁴

Target SLS roof displacement 375 mm (H/400)

Example global inertia ~ 397 m⁴

SLS period 6.26 s

ULS period 6.94 s

Adjusted SLS displacement ~ 296 mm (~ H/507)

RKALC building period tool showing separate SLS and ULS effective section inputs and first-mode periods — Example period estimates using the RKALC building-period tool: 6.26 s at SLS and 6.94 s at ULS.

03 · ULS and SLS setup

Run ultimate and serviceability wind assessments as separate design checks

The worksheet separates return period, damping and response objectives for ULS and SLS before bringing both streams back into the structural model.

Start

Review lateral system

Confirm the preliminary stiffness, mass and periods in both principal directions.

ULS

Strength response

The example notes return periods such as 1/500 or 1/1000 and higher damping assumptions.

SLS

Drift & acceleration

The example notes return periods around 1/5 to 1/10 and lower serviceability damping.

Review

Iterate if needed

Unsatisfactory drift, strength or comfort results feed back into the lateral-system review.

In both streams, WindKALC is supplied with pressure factors, directional factors, shielding and the building period in each principal direction. ULS output proceeds to along-wind and cross-wind loads for structural analysis; SLS output adds occupant acceleration and comfort assessment.

Flow chart showing the WindKALC Advanced ULS and SLS workflow from lateral-system review through ETABS and comfort checks — Typical worksheet workflow: review the lateral system, establish mass and site inputs, run ULS and SLS, then iterate if strength, drift or comfort is unsatisfactory.

04 · Occupant acceleration

Check serviceability response against an adopted comfort criterion

For this educational example, the worksheet adopts the Melbourne (1988) acceleration criterion and also shows the ISO 10137 evaluation curves for comparison.

Occupant comfort can become a controlling issue in a slender tall building even when strength and drift are otherwise manageable. The worksheet therefore treats acceleration as an explicit SLS output rather than only reviewing force and displacement.

A separate human-perception table is included in the worked example. The worksheet clearly notes that these perception levels are informative and should not be confused with the adopted occupant-comfort acceptance criterion.

Occupant acceleration criteria comparing the Melbourne 1988 criterion with ISO 10137 evaluation curves — Acceleration criteria reproduced in the worked example, with the Melbourne (1988) criterion adopted for the example.

05 · Ultimate wind calculation

Review along-wind, resonant and cross-wind response together

The ULS screen brings project inputs, directional factors, dynamic factors and response results into one view.

The example ULS calculation uses Region A, Terrain Category 3 and a 1/500 return period in the displayed WindKALC screen. Directional periods, pressure coefficients, combination factors, direction multipliers and shielding factors are entered separately for the two principal axes.

WindKALC then reports dynamic factors and directional response quantities including total base shear, overturning moment, resonant moment, cross-wind base shear, cross-wind overturning moment and acceleration. The screenshot highlights several governing response values to draw attention to the dynamic contribution.

Along-wind response Cross-wind response Dynamic factors Directional inputs

WindKALC Advanced ultimate wind calculation screen with project inputs, directional inputs and wind response results — Ultimate wind calculation screen from the worked example.

06 · Structural-model loading

Export equivalent static wind loads for Excel / ETABS

WindKALC converts the directional response into storey-by-storey equivalent static loading for structural analysis.

The worked example shows directional wind figures, response-envelope graphs and tabulated storey loading. Each directional sector includes storey height, terrain multiplier, design wind speed and equivalent horizontal force components for application to the building model.

The worksheet specifically identifies the export of equivalent static wind loads to Excel / ETABS as the next step, allowing the preliminary dynamic wind assessment to be represented by load distributions in the analysis model.

WindKALC Advanced equivalent static wind load tables and response graphs ready for export to Excel or ETABS — Directional equivalent static loading and response envelopes, with export to Excel / ETABS highlighted in the worksheet.

07 · Ultimate response envelope

Compare governing directions rather than relying on a single wind angle

The worksheet summarises representative 0, 90, 180 and 270 degree cases and plots the base-shear and overturning envelopes.

Angle 0

+Y case

Along-wind base shear: 6,020 kN
Along-wind moment: 509.2 MN.m
Cross-wind base shear: 11,887.73 kN
Cross-wind moment: 1,243.8 MN.m

Angle 180

-Y case

Along-wind base shear: 4,148 kN
Along-wind moment: 350.8 MN.m
Cross-wind base shear: 6,091.89 kN
Cross-wind moment: 637.41 MN.m

Angle 90

+X case

Along-wind base shear: 4,642 kN
Along-wind moment: 392.6 MN.m
Cross-wind base shear: 7,516.94 kN
Cross-wind moment: 786.5 MN.m

Angle 270

-X case

Along-wind base shear: 5,305 kN
Along-wind moment: 448.7 MN.m
Cross-wind base shear: 9,570.69 kN
Cross-wind moment: 1,001.4 MN.m

The response plots beneath the directional sketches make the same point graphically: the critical base shear and the critical overturning moments do not necessarily occur at the same building orientation or in the same response component.

Ultimate wind-load summary for wind angles 0, 90, 180 and 270 degrees with base shear and overturning moment graphs — Ultimate directional summary reproduced from the worked example.

08 · Serviceability wind calculation

Check drift and occupant acceleration with SLS-specific inputs

The SLS screen uses the serviceability return period, lower damping and the SLS period to assess drift-related loads and acceleration.

The displayed SLS case uses a 1/10 return period, an SLS period of 6.26 s and a damping ratio of 0.015. The output includes along-wind peak acceleration, cross-wind peak acceleration and the combined acceleration reported by WindKALC.

In this worked example, the worksheet notes that cross-wind and combined acceleration are above the adopted acceptance criterion. It therefore suggests reviewing the preliminary model inputs, including the SLS period calculation, exact mass and terrain category.

WindKALC Advanced SLS calculation showing serviceability wind response and highlighted cross-wind and combined accelerations — SLS calculation from the worked example, with cross-wind and combined accelerations highlighted for further review.

For a slender tall building, preliminary wind design is not only a strength problem: stiffness, period, cross-wind response and occupant acceleration can influence the structural system early.

The worked example uses WindKALC Advanced as an early-stage framework: establish rational preliminary building properties, assess both ULS and SLS response, export equivalent static loads to the structural model and revisit the lateral system when the response is unsatisfactory.

09 · Learning resource

WindKALC Advanced tall-building worked example

Review the complete educational worksheet, including the preliminary building model, period calculations, ULS / SLS workflow, comfort criteria, WindKALC screens and load-export examples.

Worked example · 11 pages

Wind loads on buildings using WindKALC Advanced

A compact educational example for a 150 m slender office tower, covering preliminary stiffness and periods, ULS / SLS wind response, acceleration criteria and equivalent static wind loads for ETABS.

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WindKALC Advanced ULS and SLS design workflow

Workflow summary

Use the worksheet as a preliminary design checklist

Review the lateral system, establish participating mass and periods, nominate site wind inputs, assess ULS and SLS separately, export loads to the structural model and iterate when required.

Return to workflow Open WindKALC

Worked example preview

WindKALC Advanced - wind loads on buildings

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Related tools and resources

Continue from the worked example into the WindKALC application or browse other RKALC learning resources.