Structural Analysis of a 15m Acrylic Pool Wall Failure: Calculation Method and Rebate Geometry Case Study
Engineering case study of a 15m × 1.2m rooftop acrylic pool wall originally specified at 120mm thickness and later replaced at 150mm, where deflection led to silicone delamination at the panel corners and water leakage. Root cause traced to calculation software and material property inputs, compounded by inadequate rebate depth and width on both the original and replacement panel.
A. Introduction This case study documents a 15-meter structural acrylic pool wall installation on a Dubai rooftop project delivered by New Exclusive in the firm's early years. The panel experienced excessive deflection in service. The deflection caused silicone delamination at the vertical and horizontal corners where the panel met the surrounding structure, which became the leak path. A remediation attempt using a thicker replacement panel did not resolve the failure. The engineering lessons from this case have since reshaped the firm's calculation methodology and installation detailing for long-span structural acrylic. B. Project Specifications
Application: rooftop infinity pool, long-span acrylic pool wall Panel length: 15 meters Visible water height: 1.2 meters Original panel thickness: 120mm Replacement panel thickness: 150mm Material: cell-cast PMMA Location: Dubai, UAE Installation type: top-and-bottom rebate engagement into surrounding structure Sealant: silicone (primary waterproofing component at the panel-to-structure interface)
C. The Problem
Visible outward deflection along the upper portion of the panel Silicone delamination at the left vertical corner of the panel-to-structure interface Silicone delamination at the horizontal corner where the panel meets the rebate base Water leakage tracking down the external face of the panel from the delaminated corners Failure persisted after replacement of the original 120mm panel with a 150mm panel
D. First Diagnosis The initial diagnosis pointed to panel thickness as the cause of deflection. The remediation followed that diagnosis. The 120mm panel was removed and replaced with a 150mm panel, on the assumption that the thicker panel would reduce deflection across the same span and resolve the leak. The replacement failed. Deflection continued. Silicone delamination at the corners continued. The leak path remained open. The first diagnosis was incomplete, and the second installation inherited the same engineering default as the first.
E. Root Cause Analysis The failure had two compounding causes. Both originated upstream of the panel itself. Calculation methodology. The original 120mm specification was produced using STAAD Pro with structural glass properties entered as the material inputs. STAAD Pro is structural analysis software built primarily for rigid materials. Cell-cast PMMA is a linear thermoplastic polymer, not a rigid material. The polymer responds to sustained load with elastic deformation and time-dependent creep that rigid-material software does not model. Entering glass properties into a calculation intended for PMMA produces a thickness specification built on the wrong material behavior from the first input.
A 15-meter span at 1.2 meters of visible water height also sits outside the field formula scope. The formula of water level in centimeters divided by ten equals panel thickness in centimeters applies only to villa pools, podium pools, and ground-floor pool walls up to 7 to 8 meters in length where wind load is not significant. A 15-meter rooftop pool wall is outside that scope on both length and wind exposure. The application required full <a href="https://new-exclusive.com/TARGET-URL-1">polymer-finite-element-analysis with PMMA-specific material properties</a>, including the creep coefficient, flexural modulus, modulus of elasticity, coefficient of thermal expansion, and the appropriate safety factor.
That calculation was not performed. Rebate geometry. The rebate detail used on the original installation did not match the load conditions of a long-span panel. For structural acrylic panels of this length, the rebate has to provide sufficient edge engagement to hold the panel against the hydrostatic load distributed across the span. Two rules apply together. First, rebate depth scales with panel thickness, with depth equal to approximately twice the panel thickness as the baseline. Second, rebate depth scales further with panel length beyond the standard 7-to-8-meter span. For a panel of approximately double the standard length, the rebate depth has to add approximately 100mm beyond the thickness-doubled baseline. Rebate width remains approximately 200mm.
For the 120mm original panel at 15 meters in length, the corrected rebate depth would have measured approximately 340mm. For the 150mm replacement panel at the same length, the corrected rebate depth would have measured approximately 400mm. The actual rebate detail on this project did not meet either specification, or the rebate was not revised when the panel was upgraded to 150mm.
The compounding effect: a panel specified on rigid-material assumptions, installed into a rebate that did not match the load conditions of the span, produced deflection at the top of the panel that the rebate edge engagement could not restrain. The deflection transmitted load into the silicone joint at the corners. Silicone does not have the elasticity to accommodate that magnitude of cyclic movement at the panel edge. The silicone delaminated. The leak path opened.
F. Technical Observation In long-span structural acrylic installations, panel thickness and rebate geometry have to be specified together. A correctly thickened panel installed into an inadequate rebate behaves as if the panel were under-specified. Rebate depth scales with two variables: panel thickness as the baseline rule (depth equal to approximately twice the panel thickness), and panel length beyond the standard span as the second rule (additional depth added for spans beyond 7 to 8 meters). Calculation software and material property inputs are equally part of the same engineering chain. PMMA cannot be calculated as if it were glass.
G. Proposed Solution The corrective approach for this case involved three elements working together. First, a new structural calculation using polymer-FEA software with PMMA material properties entered correctly. The load case integrated hydrostatic pressure across the full 1.2-meter water height, wind load for the rooftop exposure, and the panel's own self-weight. The creep coefficient and PMMA modulus values were taken from the manufacturer-certified data sheet of the production lot.
Second, a revised rebate detail engineered to match the recalculated panel thickness and the panel length. Depth scaled by two rules together: approximately twice the panel thickness as the baseline, with additional depth added for the span beyond 7 to 8 meters. For this 15-meter, 150mm panel the corrected rebate depth lands at approximately 400mm. Width approximately 200mm to seat the panel cleanly with installation tolerance and silicone reservoir. Indexing reviewed to confirm uniform edge engagement across the full panel length.
Third, removal of the existing 150mm panel, reconstruction of the rebate to the revised geometry, and re-installation with the calculation-driven panel specification. H. Key Engineering Lesson In long-span structural acrylic, thickness alone does not carry the panel. Calculation software, material property inputs, panel thickness, and rebate geometry are one system. A weakness in any one element produces failure at the joint, and the joint is the leak.
I. Transparency Note This was a New Exclusive project from the firm's early years. The calculation was performed in-house using STAAD Pro with glass properties applied to a PMMA panel, and the installation followed manufacturer-supplied detailing without independent verification of the rebate geometry against the long-span load condition. The thickness specification was wrong because the calculation method was wrong. The replacement attempt failed because the rebate was not revised in step with the panel upgrade.
New Exclusive owns this case directly. The lessons reshaped how the firm now approaches structural calculation, software selection, material property inputs, and rebate engineering for every long-span project that has followed. The firm's current practice requires polymer-FEA with PMMA-specific properties, independent verification of supplier calculations, and rebate detailing specified jointly with the panel thickness and the panel length. <a href="https://new-exclusive.com/TARGET-URL-2">10-year leak-proof installation guarantee</a> and the 30-year no-color-change guarantee on premium acrylic blocks now backing every New Exclusive project are the commercial expression of the discipline this case made unavoidable.
J. Conclusion The 15-meter pool wall case demonstrates that successful structural acrylic engineering depends on the relationship between calculation methodology, material property accuracy, panel thickness, and installation geometry rather than thickness alone. A panel specified by the wrong software with the wrong material inputs and installed into a rebate that does not match the load conditions of the span will fail at the joint, regardless of how thick the panel is made in remediation. The case is field documentation of why polymer-specific calculation and rebate-thickness alignment are not refinements to the structural acrylic process. They are the structural acrylic process.
About the Author Rabih El Hawarni is the Structural Acrylic Specialist and Founder of New Exclusive Decoration Design & Fit-Out LLC, Dubai. New Exclusive delivers structural cell-cast PMMA pool walls, underwater windows, panoramic pool floors and cantilevered installations across the UAE and the wider GCC, with a ten-year leak-proof installation guarantee and a thirty-year no-color-change guarantee on the premium acrylic blocks used.