Finite Element Analysis of Plain Cement Concrete Slab with and Without Opening

Abstract

In modern construction practices, plain cement concrete (PCC) slabs are often designed with openings to accommodate services such as electrical conduits, plumbing, and ventilation ducts. However, the introduction of openings leads to significant changes in the structural behavior of slabs, including increased deflections, stress concentrations, and potential early cracking. This research presents a comprehensive finite element analysis (FEA) study on PCC slabs with and without openings, considering different concrete grades (M20, M30, M40, and M60). The slabs were modeled under simply supported conditions and subjected to a uniform distributed load. Various parameters were analyzed, including opening size and location.

Introduction

I. Overview

Plain Cement Concrete (PCC) slabs are widely used in construction due to their simplicity, cost-effectiveness, and durability, especially for pavements, floors, and low-load structures. As sustainability and efficiency demands increase, innovations such as pre-designed hollow openings are gaining attention to reduce material usage, integrate utilities, and decrease self-weight—especially in high-rise buildings.

II. Benefits of Hollow Openings in PCC Slabs

• Structural Efficiency: Reduces slab self-weight, beneficial in tall structures.

• Integration of Services: Allows MEP (Mechanical, Electrical, Plumbing) installations without drilling.

• Sustainability: Less cement and aggregate lowers environmental impact (embodied carbon).

III. Challenges

• Stress Concentrations: Hollow areas can introduce crack-prone zones due to altered load paths.

• Reduced Load Capacity: Openings may lower tensile and shear resistance, risking structural failure.

• Requires experimental and numerical analysis to assess safety and performance.

IV. Key Properties of PCC Slabs

• Material: Cement, water, sand (fine aggregate), gravel/crushed stone (coarse aggregate).

• Unreinforced: Lacks steel reinforcement, hence low tensile strength.

• Typical Applications: Sidewalks, driveways, sub-bases, and residential floors.

V. Advantages & Limitations

? Advantages:

• Cost-effective (no rebar).

• Durable under compression.

• Easy to install and low maintenance.

? Limitations:

• Poor tensile strength.

• Susceptible to cracking under thermal changes or settlement.

VI. Literature Review Highlights

1. Jofriet & Gregory (1971) – Finite element analysis (FEA) of RCC slabs; discussed methods for flexural rigidity in cracked regions.

2. Mosallam & Mosalam (2003) – FRP repair of concrete slabs; found 500% strength improvement in unreinforced slabs.

3. Foster et al. (2004) – Studied membrane action in reinforced slabs; observed much higher load capacity than predicted.

4. Thanoon et al. (2005) – Compared 5 repair techniques (epoxy, grout, FRP, etc.) for cracked slabs; all methods enhanced structural capacity.

5. El-Sayed et al. (2005) – Tested shear strength of FRP-reinforced slabs; ACI guidelines were conservative, better predictions from JSCE and CAN/CSA codes.

VII. Methodology

1. Experimental Testing

• Specimen: 500×200×50 mm PCC slabs using M40 concrete.

• Test: Three-point flexural load after 28 days of curing.

• Standard: IS:9399 – 1979; Load rate of 1.8 kN/min.

2. Numerical Modeling (FEM)

• Software: ABAQUS 6.14 used for Finite Element Modeling (FEM) of 3D slab models.

• Stages of FEM:

  • Pre-processing: Geometry, materials, mesh generation.

  • Processing: Load application, boundary conditions, simulation.

  • Post-processing: Visualization of results (e.g., stresses, cracks).

VIII. Research Objective

To analyze the effect of different types of hollow openings in PCC slabs on their load-bearing capacity, especially considering different concrete grades. The aim is to:

• Develop a validated FEM model.

• Examine structural performance under loading.

• Compare experimental and simulation results.

IX. Problem Statement

Although PCC is widely used, it lacks tensile strength and is prone to cracking—especially when modified with openings. This study investigates how various opening shapes and concrete grades affect the slab's structural performance. The goal is to support design improvements and enhance the structural reliability of modern PCC slabs.

Conclusion

This study provides a comprehensive analysis of the impact of openings on the load-carrying capacity of P.CC slab, offering practical insights for improving precast P.C.C panel and construction practices. The FEA approach enables a deeper understanding of structural behavior, contributing to the development of more P.C.C slab panels. • By increasing the grade of concrete on the P.C.C slab the load carrying capacity of P.C.C slab also increases. • Circular openings at different locations lead to a reduction in the load-carrying capacity of P.C.C slab, and by increasing the size of opening a significant decrease in load carrying capacity is also observed. • Reduction of area on concrete in tension zone also leading to greater reductions in load carrying capacity of P.C.C slab panel. • The location of opening also affects the load carrying capacity of P.C.C. slab panel. • Higher grades of concrete slab panel have higher resistance against opening as compared to lower grade of P.C.C slab panel. • Opening at or near NA gives better results compared to openings away from NA. The following are the suggestions for further study of the present work: • The analysis can be made on P.C.C slab panel with wire mesh, poly vinyl fiber and other types of tensile strength improving material with openings. • The analysis can be made on P.C.C slab panel with openings above NA. • The analysis can be made on P.C.C slab panel with openings that are rectangular in shape instead of circular.

References

[1] Jofriet, Jan C. and G. M. Mcneice. (1971). “Finite Element Analysis of Reinforced Concrete Slabs.” Journal of the Structural Division 97 (1971): 785-806. [2] Bureau of Indian Standards. (1979). IS 9399:1979 - Specification for flexible polyurethane foam for domestic mattresses. New Delhi: Bureau of Indian Standards. [3] Bureau of Indian Standards. (2000). IS 456:2000 - Plain and reinforced concrete – Code of practice. New Delhi: Bureau of Indian Standards. [4] Mosallam, A. S., & Mosalam, K. M. (2003). Strengthening of two-way concrete slabs with FRP composite laminates. Construction and Building Materials, 17(1), 43–54. https://doi.org/10.1016/S0950-0618(02)00092-2 [5] Foster, S. ., Bailey, C. ., Burgess, I. ., & Plank, R. . (2004). Experimental behavior of concrete floor slabs at large displacements. Engineering Structures, 26(9), 1231–1247. https://doi.org/10.1016/j.engstruct.2004.04.002 [6] Thanoon, W. A., Jaafar, M. S., A. Kadir, M. R., & Noorzaei, J. (2005). Repair and structural performance of initially cracked reinforced concrete slabs. Construction and BuildingMaterials, 19(8), 595–603. https://doi.org/10.1016/j.conbuildmat.2005.01.011 [7] El-Sayed, A., El-Salakawy, E., & Benmokrane, B. (2005). Shear Strength of One-Way Concrete Slabs Reinforced with Fiber-Reinforced Polymer Composite Bars. Journal of Composites for Construction, 9(2), 147–157. https://doi.org/10.1061/(ASCE)1090-0268(2005)9:2(147) [8] Bureau of Indian Standards. IS 516 (2021)- Flexural testing of concrete beams – Code of practice. New Delhi: Bureau of Indian Standards.

Copyright

Copyright © 2025 Mohd Anas Khan, Dr. Saleem Akhtar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.