ANALISA STRUKTUR GEDUNG UNSYMMETRIC-PLAN DENGAN MODAL PUSHOVER ANALYSIS (MPA) PADA STRUKTUR BETON BERTULANG

Bambang Budiono¹ dan M. Albar Daen²

ABSTRAK

Struktur tidak simetris dalam arah tapak, dapat diklasifikasikan menjadi tiga sistem, unsymmetric-plan Torsionally-stiff system; unsymmetric-plan Torsionally-similarly-stiff system; dan unsymmetric-plan Torsionally-flexible system. Nonlinear Response History Analysis (NLRHA) adalah suatu analisis yang dikembangkan untuk mengestimasi seismic demand dan kapasitas struktur secara akurat. Mengingat perhitungan NLRHA yang menggunakan analisis riwayat waktu non-linier sangat kompleks, maka perlu dilakukan metoda pendekatan untuk menganalisis seismic demand dari struktur, yaitu dengan Modal Pushover Analysis (MPA).Respon final MPA didapat dari masing-masing mode yang dikombinasikan dengan metoda Complete Quadratic Combination (CQC) pada percepatan gempa yang sama. Berdasarkan studi pada struktur beton bertulang 10 lantai untuk sistem portal terbuka ,maka dapat disimpulkan bahwa metode MPA dapat digunakan untuk menggantikan metode NLRHA dengan penambahan kontribusi mode yang lebih tinggi. Dari hasil hasil analisis MPA secara keseluruhan konservatif terhadap NLRHA untuk sistem struktur unsymmetric-plan Torsionally stiff system dan unsymmetric-plan Torsionally flexible system. Tetapi pada system struktur unsymmetric-plan Torsionally similarly stiff system analisis MPA tidak konservatif terhadap analisis NLRH. Ini disebabkan mode-mode awal sangat dipengaruhi oleh Translational dan juga rotasional sehingga sulit di uncoupled kan. Fenomena ini terjadi karena respon total terjadi secara simultan antara translasional dan rotasional.

Kata kunci : Unsymmetrical-Plan, Non-Linear Response History Analysis, Modal Pushover Analysis, Seismic Demand, Torsionally-Stiff, Torsionally-Similarly-Stiff, and Torsionally-Flexible Systems, Single Degree of Fredom System.

ABSTRACT

The unsymmetrical plan of a structure is categorized into three systems, namely Torsionally-Stiff, Torsionally-Similarly-Stiff, and Torsionally-Flexible Systems. The Nonlinear Response History Analysis (NLRHA) is an analysis that is able to predict the seismic demand and capacity of structures accurately. Because of the NLRHA complexity, the study is conducted using the Modal Pushover Analysis (MPA) approach in analyzing the seismic demand of structures, which is less complex. The MPA improves the conventional static pushover analysis namely the Capacity Spectrum Method (CSM), where in the MPA method, the contribution of higher modes of the structure is taken into account not only first mode as in CSM. The total response of MPA is obtained from the combination of each mode response using the Complete Quadratic Combination (CQC) method. As a result of the study for the 10 story building of reinforced concrete frames, it was found that the MPA method can be used to replace the NLRHA method. Based on the results of the MPA method, it is concluded that the MPA method is conservative compared to NLRHA method both for the Torsionally-Stiff and Torsionally-Flexible Systems. However, for the Torsionally-Similarly-Stiff system, in the cases of 10 story structure, the MPA method is not in a good agreement with the NLRHA. For the final remarks, the MPA can be used to replace the NLRHA provided the elastic modes are not strongly coupled. This phenomena occurs when the fundamental periods of the Translation and Rotation modes are closely related.

Keywords: Unsymmetrical-Plan, Non-Linear Response History Analysis, Modal Pushover Analysis, Seismic Demand, Torsionally-Stiff, Torsionally-Similarly-Stiff, and Torsionally-Flexible Systems, Single Degree of Fredom System.

1) Staf Pengajar, Kelompok Keahlian Rekayasa Struktur, Teknik Sipil FTSL ITB

2) Mahasiswa Program Magister Rekayasa Struktur Program Studi Teknik Sipil FTSL ITB