📄 MasterSeries Solutions for Domestic Alterations and Refurbishments

MasterSeries Solutions for Domestic Alterations and Refurbishments

Domestic alterations and extensions - such as forming large ground-floor rear openings for open-plan living, inserting loft dormers, or constructing basement extensions, are among the most frequent projects for UK structural engineering practices. However, modifying low-rise loadbearing masonry structures involves significant structural stability and soil-structure interaction risks. It is insufficient to size lintels or beams in isolation; engineers must trace the full load path down to the supporting foundations.

This guidance note addresses the technical challenges in domestic structural design and explains how to implement solutions using MasterSeries, including advanced substructure modeling with soil spring supports and Finite Element (FE) surfaces.

1. Global Sway Stability & Deflection Envelope Controls

The Challenge

When a ground-floor rear masonry wall is removed, a domestic building loses its independent out-of-plane lateral masonry stability. Engineers must introduce a restorative lateral stability system - typically a goalpost frame (2 moment connections) or a box frame (4 moment connections).

In these frames, lateral sway stiffness and serviceability deflection limits (SLS) almost always govern member section selection over ultimate limit state (ULS) bending strength. Supporting delicate architectural elements, such as full-height bi-fold glazing, often requires restricting live-load vertical deflections to tight absolute limits (e.g. 3 mm).

--Image of: --Domestic Steel Moment Frame Diagram

[Figure 1: Domestic Steel Moment Frame Diagram - Goalpost frame load path, moment connections, and sway stability under lateral wind loading]

MasterSeries Implementation

  • 2D Frame Analysis: Model 2D goalpost or box frames in MasterFrame using standard UC/UB section profiles. Floor and roof gravity area loads are automatically distributed to frame members.
  • Deflection Limits: In MasterKey Steel Design, configure custom member deflection briefs, combining relative span limits (e.g. \(L/360\)) with absolute millimeter caps.
  • Section AutoDesign: Use Section AutoDesign with Sort by Weight enabled. MasterSeries automatically identifies the lightest steel section that satisfies both strength and deflection criteria.

2. Modeling Partial Base Fixity & Concentrated Reactions

The Challenge

Forming large openings converts original continuous masonry line loads into concentrated point loads and overturning moments at frame column bases. Standard ULS design assumes pinned column bases, but accounting for partial base stiffness can help reduce frame sway and total beam deflection.

MasterSeries Implementation

  • Dummy Member Base Fixity: To model partial column base fixity for sway stability without over-estimating foundation fixity, model dummy members at column bases in MasterFrame. Set \(I_{\text{Dummy}} = 0.1 I_{\text{column}}\) or \(0.2 I_{\text{column}}\) with a length of \(L_{\text{Dummy}} = 0.75 L_{\text{column}}\) and pinned extreme ends.
  • Pad Foundation Checks: Base reactions populate MasterKey Concrete Pad Foundations, which verifies soil bearing pressures under combined axial load, shear, and bi-axial overturning moments. The module also carries out base uplift checks and stability factors against overturning and sliding.

3. Modeling Ground Beams Supported on Soil (Spring Supports)

The Challenge

When using a box frame, the bottom chord acts as a ground beam transferring column base moments and vertical forces into the ground. Modeling a ground beam on continuous soil requires accounting for soil-structure interaction, as stiffer soils attract higher localized bearing pressures near columns while stiffer beams distribute loads more evenly.

--Image of: --Ground Beam & FE Raft Soil Spring Supports Diagram

[Figure 2: Ground Beam & FE Raft Foundation Diagram - Soil spring supports (\(K_s\)), subgrade modulus, column reactions, and attached concrete beam elements]

MasterSeries Implementation (Line Ground Beams)

📄 Modelling Ground Beams Supported on Soil in MasterFrame

  • Analytical Segmentation: In MasterFrame, split the continuous ground beam into shorter analytical elements by introducing intermediate nodes.
  • Nodal Vertical Spring Supports: Apply vertical spring supports to each intermediate node.
  • Soil Spring Stiffness Calculation: Calculate vertical spring stiffness (\(k\)) based on soil subgrade modulus (\(K_s\)) and spring tributary area (\(A_{\text{trib}}\)): \[k = K_s \times A_{\text{trib}}\] (Where \(K_s = \frac{\text{Allowable Bearing Pressure}}{\text{Allowable Settlement}}\)).
  • Non-Linear Iterative Analysis: MasterFrame performs a non-linear iterative analysis to distribute beam loads into the soil springs based on relative beam and soil stiffness.

4. FE Surfaces for Domestic Rafts & Strip Foundations

The Challenge

Where low bearing capacity soils, high concentrated loads, or boundary constraints prevent the use of traditional pad footings, engineers frequently design continuous reinforced concrete strip footings or raft slabs.

MasterSeries Implementation (FEA & Attached Beams)

📄 Strip Foundations

  • FE Surface Modeling: In MasterFrame FEA, create a 2D Finite Element surface representing the slab or raft centerline.
  • Compression-Only Subgrade Modulus: Apply a full-area vertical spring support to the FE surface using the soil subgrade modulus (e.g. \(12,000\text{ kN/m}^3\)), set to Compression Only to prevent unrealistic tension in soil.
  • Corner Restraints for Stability: To prevent rigid-body sliding without over-restraining the slab, apply translational \(X\) and \(Z\) restraints to one corner node, and an \(X\) or \(Z\) restraint to an adjacent corner.

  • Attached Concrete Beam Method: For strip footings or stiffened raft ribs, draw a 1D member along the FE surface centerline and set it as an Attached Beam.

    • Assign the attached beam zero stiffness (\(E=0, G=0\)) and zero self-weight so the FE surface handles all structural stiffness without double-counting.
    • Export analysis forces from the attached beam to MasterKey Concrete Beam Design to detail and schedule longitudinal and shear reinforcement.

5. Justifying Retained Masonry Shear Walls (Yield Line Method)

The Challenge

Retaining partial masonry return walls or buttressing piers can avoid the need for full steel moment frames. However, traditional linear elastic code checks for laterally loaded masonry with multiple door and window openings are often overly conservative.

MasterSeries Implementation

  • Advanced Yield Line Analysis (AYLA): MasterKey Masonry Design uses an iterative yield-line virtual work algorithm to evaluate out-of-plane lateral panel capacities.
  • Complex Openings: Model masonry panels containing up to 10 openings (windows, doors) alongside vertical wind posts. AYLA evaluates the true yield-line failure mechanism, helping engineers justify existing host walls.

Step-by-Step MasterSeries Domestic Design Workflow

  1. Geometry & Loading: Import architect DXF plans into MasterFrame, set up grid lines/levels, and generate 2D/3D frame geometry. Apply Dead (D1), Live (L1), and Wind (W1) load cases.
  2. Member Sizing: Run a Static Elastic Analysis, open MasterKey Steel Design, set deflection limits, and execute Auto Size Current View.
  3. Connection Checks: Open MasterKey Moment & Simple Connections to check extended end-plate beam-column joints, base plates, and Eurocode tie forces (disproportionate collapse).
  4. Masonry & Substructure: Verify host return walls using MasterKey Masonry. Transfer column reactions into MasterKey Concrete Pads or model continuous ground beams/rafts on vertical soil springs in MasterFrame FEA.

PowerPad / MasterSeries Lite Suite Awareness

Many small practices perform residential refurbishments using PowerPad (MasterSeries Lite Suite). PowerPad provides access to lite versions of core modules, including 2D/3D MasterFrame analysis, simple and moment connections, steel member design, masonry design, and pad foundations.

Key PowerPad limits to recognize for domestic projects:

  1. Member Limits: PowerPad 200 is limited to 200 MasterFrame members, while PowerPad 500 allows up to 500 members.
  2. FE Surface Limit: Standard PowerPad FE functionality is limited to 1 FE surface up to 200m². Multiple FE surfaces or larger raft foundations require the FE Analysis upgrade.
  3. Masonry Design: PowerPad includes the Lite version of Masonry Design. Advanced Yield Line Analysis (AYLA) requires the full Masonry Design module add-on.
  4. Concrete Slab & Wall Design: Concrete Slab & Wall Design is not included as standard and requires an add-on to design reinforcement from FE results.

You may be reaching one of the PowerPad / MasterSeries Lite Suite limits. PowerPad is designed as a Lite suite, so some larger models or advanced workflows require an upgrade or additional module. I recommend contacting MasterSeries support/sales at help@masterseries.com or sales@masterseries.com or calling 02890 36595, so they can review your licence and advise on the most suitable option.

Rather than changing your workflow manually or using workarounds, it may be worth asking MasterSeries whether an upgrade, trial or short-term rental would be suitable. This can be particularly useful if you are regularly transferring loads, reactions or design forces between separate programs. Because you already have the analysis model in MasterFrame, additional integrated modules can help reduce manual load transfer between programs. This can save time when checking steel members, concrete beams and columns, foundations, pile caps, steel connections, slabs and walls, especially when the frame changes and design forces need to be updated.

Engineering Responsibility & Recommended Escalation

Engineering Responsibility Reminder

Please note: MasterSeries software outputs provide structural analysis calculations and code verification checks based on user input. Overall engineering assumptions, site survey accuracy, condition assessment of existing host masonry, temporary works sequencing (propping/needling), and Party Wall Act compliance remain the sole responsibility of the competent structural engineer.

Recommended Escalation Message

Please contact sales@masterseries.com with your licence details and a short description of what you are trying to model or design. The team can confirm whether this is possible within your current licence, or whether a trial, rental or upgrade would be more suitable.