[Design Talk #1] Optimizing Structural Systems in Real Projects: Flat Slabs, Precast Balconies & Retaining Walls

In this article, we present a detailed breakdown of a representative civil project executed by Pontech – covering both the structural design approach and the on-site coordination process.

As part of Pontech’s internal Design Talk #1, the engineering team discussed technical challenges and shared their solutions involving flat slabs, precast balconies, and temporary retaining walls. The talk also highlighted valuable structural design lessons aligned with international codes and practices.

Pontech engineers discussing structural design options during Design Talk

1. Case Study Analysis – Social Housing & General/Acupuncture Clinic Project

1.1. Project Overview

• Total Floor Area: 15,400 m²
• Scope: 4 blocks (A, B, C, D), each with 1 basement, 1 ground floor, 3 upper floors
• Pontech’s Involvement:
  • Structural analysis
  • Formwork drawing development
  • Rebar detailing

3D overview of social housing and clinic project with 4 structural blocks

1.2. Key Technical Challenges

• Maximizing usable floor area
• Reducing material quantities without compromising safety
• Simplifying site execution and minimizing construction duration

1.3. Structural Solution: Flat Slab System

• Eliminated intermediate beams, enabling direct slab-to-column load transfer
• Increased slab thickness from 200mm to 250–280mm in column-adjacent zones
• Adopted flat slabs to minimize MEP coordination conflicts and improve headroom
• Reduced construction time by simplifying formwork and eliminating beam casting

Outcome: Reduced floor height, faster execution, and improved coordination with architectural and MEP systems.

Switching from Beam-Slab to Flat Slab Systems to Reduce Floor Height and Optimize Construction

1.4. Special Structural Components

Precast Balconies

• Modular design with standard units (BA-D4, BA-D5)
• Integrated slope of 1.4% and drainage channel at edge
• Torsional and eccentric moment checks at slab-balcony connections

The precast balconies were designed using standardized modules with a 1.4% slope and integrated drainage edge detail.

Retaining Walls

• Voile VPP walls with base beams for additional support
• Temporary mat foundations ensuring stability during basement works
• Underground struts resisting lateral loads and overturning forces

Retaining wall model with Voile VPP and foundation beam support

1.5. Site Coordination: A Critical Success Factor

• Design engineers stayed in close communication with site engineers
• Continuous model updates during basement execution
• Proactively resolved potential conflicts between drawings and field conditions

Construction photo of basement level during retaining wall and rebar installation

2. Key Engineering Lessons

Punching Shear Control (Flat Slabs)

• Punching shear is critical at column heads
• Slab thickness was increased and shear reinforcement added around columns
• Load analysis was detailed to verify stress within permissible limits

References: Eurocode 2 – EN 1992-1-1 (6.4.4), ACI 318-19 (22.6.5)

Deflection Control

• Total allowable deflection: L/250, or L/500 if aesthetics or partitions are affected
• Additional reinforcement placed at slab edges using Grade A500 steel
• Long-term deflection assessed with consideration for creep and shrinkage

Reference: EN 1992-1-1, Clause 7.4.1

Precast Balcony Installation

• Torsion and eccentric loads evaluated at slab connections
• Use of steel embedment plates and supplemental bars
• Drainage components pre-installed to avoid water infiltration

Reference: PCI Design Handbook (8th Edition)

Retaining Wall Stability

• Design addressed sliding, overturning, and bearing capacity
• Lateral loads modeled in SAP2000 with manual verification
• Monolithic foundation beams ensured even load transfer

Reference: NAVFAC DM-7.2

BIM Coordination Benefits with Flat Slabs

• Eliminated beam obstructions simplified MEP routing
• Cleaner Revit/Navisworks models facilitated multi-disciplinary coordination
• Reduced design clashes and increased team efficiency

Reference: Autodesk University – Flat Slab & BIM Integration

3. Conclusion

Design Talk #3 showcases Pontech’s ability to apply tailored structural solutions rooted in real-world constraints and modern engineering practice. With flat slabs, precast balconies, and advanced retaining wall design, the team demonstrated efficiency in design and execution while aligning with international standards.

This project exemplifies the mindset of modern structural engineers: balancing technical rigor, constructability, and overall project effectiveness.