Pengaruh Penggunaan Expanded Polystyrene (EPS) Geofoam pada Raft foundation terhadap Reduksi Perpindahan Lateral (Studi Kasus: Rumah Instan Struktur Baja)

Az Zahra Qurrotul Akyun, Dr. Eng. Sito Ismanti, S.T., M. Eng

2025 | Skripsi | TEKNIK SIPIL

Bangunan Rumah Instan Struktur Baja (RISBA) merupakan tipe rumah sederhana yang memiliki tujuan untuk mempercepat rehabilitasi rumah rusak terdampak bencana gempa bumi. Sebagai elemen struktur bawah, bangunan RISBA menggunakan fondasi konvensional berupa raft foundation beton bertulang yang berfungsi untuk mendistribusikan beban bangunan ringan secara merata ke tanah dasar. Namun, pada kondisi tanah pasiran yang rentan kehilangan kekuatan akibat guncangan gempa, diperlukan inovasi tambahan yang mampu mengurangi tekanan kontak sekaligus meningkatkan stabilitas sistem fondasi. Salah satu material alternatif dalam hal ini adalah Expanded Polystyrene (EPS) Geofoam. Penelitian ini bertujuan mengidentifikasi kemampuan EPS Geofoam sebagai material komplementer pada raft foundation untuk mereduksi displacement lateral arah-x maupun arah-y. 

Penelitian dilakukan dengan memodelkan raft foundation tanpa EPS Geofoam maupun dengan EPS Geofoam menggunakan software MIDAS GTS NX 3D. Pemodelan divariasikan pada aspek kepadatan tanah (loose, medium dense, dense), jenis EPS (EPS15, EPS22, EPS29), jenis pembebanan (statis, pseudostatis) dan  lima desain peletakan EPS Geofoam.

Hasil simulasi menunjukkan bahwa EPS Geofoam mampu mereduksi displacement lateral secara signifikan. Desain 4 paling optimal, dengan reduksi hingga 91% (arah-x) dan 97% (arah-y) pada beban statis, serta 77% (arah-x) dan 52% (arah-y) pada beban pseudostatis. Efektivitas tertinggi dicapai pada tanah pasir berkepadatan tinggi, sementara variasi densitas EPS tidak berpengaruh besar terhadap reduksi deformasi.

Rumah Instan Struktur Baja (RISBA) is a project developed as a practical solution to accelerate post-disaster housing rehabilitation. Generally, RISBA uses a raft foundation formed by reinforced concrete as its substructure element. However, when the ground is dominated by sandy soils that are sensitive to strength reduction caused by earthquakes, design enhancements are required to improve the stability of raft foundation. A viable alternative that has shown considerable potential is Expanded Polystyrene (EPS) Geofoam. The effectiveness of EPS Geofoam as a supplementary foundation material is investigated through its impact on lateral displacement reduction in both x- and y-directions. 

Utilizing MIDAS GTS NX 3D software for numerical analysis, this study compares the behavioral responses of raft foundations incorporating EPS Geofoam against conventional designs. The comprehensive evaluation framework includes variations across soil density categories (loose, medium dense, and dense), EPS Geofoam densities (EPS15, EPS22, and EPS29), load type (static and pseudostatic), and five distinct EPS placement strategies.

This study indicates that EPS Geofoam significantly reduces lateral displacement, with Design 4 (EPS Geofoam arranged at fixed distances along the x-direction) identified as the most effective configuration. Under static loading, this design achieved reductions of 91% in the x-direction and 97% in the y-direction. Under pseudostatic conditions, notable reductions continued to occur with displacement reductions of 77% (x-direction) and 52% (y-direction). Overall, EPS Geofoam proved most effective in dense sandy soils, while variations in EPS density had a negligible impact on the reduction of lateral displacement.

Kata Kunci : EPS Geofoam, raft foundation, displacement lateral, tanah pasir, MIDAS GTS NX.