Response Analysis Of The Lower Structure Of Girder Bridge With Lead Rubber Bearing (LRB) And High Damping Rubber Bearing (HDRB) Due To Earthquake Excitation

Seismic isolation is a system to reduce seismic energy acting on the bridge by adding an object so-called base insulator. The purpose of this study is to obtain a comparison of dimension, damping ratio, and the lower structure response designed as a ductile component with High Damping Rubber Bearings (HDRB) and Lead Rubber Bearings (LRB). This study uses CSI BRIDGE 21 computer program. Earthquake forces analysis uses dynamic analysis with response spectra as final evaluation for the performance of lead rubber bearing and high damping rubber bearings and the load characteristics for bridges is following SNI 1725: 2016 and bridge design for earthquake load is following SNI 2833: 2016. The bridge performance is expected to no longer rely merely on the dimensions and stiffness of the pillars in response to earthquake loads, but also on LRB or HDRB as a structural device on bridge support by increasing the effectiveness of pillar stiffness in providing damping energy during an earthquake.


Introduction
A bridge is an essential infrastructure that serves to connect two segments of road separated by obstacles, such as valley, river, ravine, irrigation and drainage channel, railroad, reservoir, and others to facilitate land transportation.
A natural disaster, like earthquakes, is one of the factors that can damage building structures. Indonesia is very prone to earthquakes due to its position on the encounter of the world's three main plates: Eurasia, Indo Australia, and Pacific. In early August 2018, an earthquake with magnitudes of 7 occurred in Lombok, West Nusa Tenggara. It proves that Indonesia has high potential and risk of earthquakes. This natural event caused a lot of damage to infrastructures, as happened to Tampes Bridge in Lombok that connects Bayan with Kayangan District, Lokok Duren Bridge that connects Kayangan and Gangga District, and LUK Bridge in Gangga District. Bridges generally get damaged in lower structures.
So far, building structural design is conventional as passive structures that only rely on stiffness and strength to bear gravity and earthquake loads. Therefore, structural performance are commonly judged by the stiffness and strength of the structure, and if it continues happen, the problem in near future is that high material demands will increase to produce a very stiff structure and eventually the construction cost will be more expensive. Technological development has created a lot of innovations that have brought positive changes in the construction world.
In recent years, base isolation has developed as a technology to design buildings and bridges in highly prone earthquake zones. The idea of base Isolation is to eliminate destruction and damage to buildings or bridges during an earthquake (Widodo et al., 2003) Based on SNI 2833-2016 regarding earthquake resistance design codes for bridges, for force-based design, where the structure is made to behave flexure to earthquake loads and the structure is allowable to get damaged in large earthquakes but not allowable to reach failure, is by determining the structural component points with the plastic hinges meet the detailing requirements in the regulations and also outside the plastic hinge to bear shear capacity. Based on the bridge structure characteristics, construction engineers can use one of three options for an earthquake design strategy, as follows: Type 1: ductile lower structures with elastic upper structures. Tipe 2: elastic lower structures with ductile upper structures. Tipe 3: elastic upper structure and lower structure with fusion mechanism on the surface between the upper and lower structures.
Base insulator types include High Damping Rubber Bearing (HDRB) and Lead Rubber Bearing (LRB). One of the bridges in Indonesia that uses Lead Rubber Bearing (LRB) is Kali Kenteng Bridge in Semarang-Solo Highway project. The bridge uses 2 LRB rows at the bottom of each girder with the system changed to a simple beam by a linked slab (Wahyuningsih Tri Hermani, 2019) This thesis will analyze the comparison of Lead Rubber Bearing (LRB) and High Damping Rubber Bearing (HDRB) on Coal Hauling Road Bridge in Belayan River, Tabang, Kutai Kartanegara -East Kalimantan related to earthquake loads.

Methodology
The research method is an analytical method for the bridge structure modeling with base isolation referred to applicable regulations, like Indonesian National Standard (SNI).
This research method uses a case study analysis. Primary data collection in the form of site condition was conducted with a direct field survey by the team to the construction site and the survey results were compiled in a report. Secondary data in the form of topographic, vehicle types, and allowable loads are obtained from the project owner's archives.
The data that has been collected is then processed as material for a bridge design study, the process is predesigned with modeling and after that a structural analysis is carried out. The results of the analysis will bereported as a form of conclusions in the study. VOLUME 21 │ NUMBER 01 │ JULY 2021 https://ejournal.worldconference.id/index.php/neutron E-ISSN: 2685-3272 | P-ISSN 1412-0860  The structure is a continuous span bridge whose length is 60m. A bridge that has 2 (two) pillars with a height (Hpier) = 8 meters. The bridge with a total concrete deck width of 8.5m, has 2 lanes with 3.5m width each and is equipped with 0.5m wide pedestrian access on both sides.

Result and Analysis
The model in this study is an initial design of a bridge structure with a span length and pier height which will later represent the actual model of the bridge structure. In this stage, the model is given a load in accordance with the provisions in SNI 2833/2016 and SNI 1725 2016. This bridge is assumed to be an important bridge and is in a strong earthquake area so that the structural design must provide sufficient dissipation energy so that the bridge structure can still be used after the earthquake ends. . Bridge modeling, in this stage modeling is carried out with the help of the CSi Bridge 21 program. VOLUME 21 │ NUMBER 01 │ JULY 2021 https://ejournal.worldconference.id/index.php/neutron For strain and stress parameters modeling reinforcing steel for the purposes of curvature moment analysis refers to CALTRANS. From the input of earthquake response spectrum data in Padang city with soft soil conditions using Csi Bridge 21 software. As shown in Figure 5 is a spectrum response spectrum in Padang city. VOLUME 21 │ NUMBER 01 │ JULY 2021 https://ejournal.worldconference.id/index.php/neutron E-ISSN: 2685-3272 | P-ISSN 1412-0860 Earthquake Base Shear Force From the CSi Bridge output results, the base reaction due to the nominal earthquake is obtained, namely for the X or longitudinal direction of 3220,729 kN and the Y or transverse direction of 7937,228 kN as shown in Figure 6 for the X and Y directions. In the loading analysis on the bridge structure model, a combination of loading with a factor scale is applied so that it can analyze in ultimate conditions or service conditions, as for the combination of loading The load combination used is based on SNI 1725: 2016 article 6.1. Table 3 shows the load combinations used are as follows Arah X Arah y VOLUME 21 │ NUMBER 01 │ JULY 2021 https://ejournal.worldconference.id/index.php/neutron E-ISSN: 2685-3272 | P-ISSN 1412-0860  Lead Rubber Bearing modeling uses products from Bridgestone with the following dimensions VOLUME 21 │ NUMBER 01 │ JULY 2021 https://ejournal.worldconference.id/index.php/neutron E-ISSN: 2685-3272 | P-ISSN 1412-0860 The results of the analysis input from the CSi Bridge program are obtained as follows In the High Damping Rubber Bearing analysis, the calculation steps for the design parameters are the same as for lead rubber bearings referring to the provisions of the Specification for Seismic Isolation Design AASHTO LRFD Brigde-2017 and Guide Specification for Seismic Isolation Design, 2012. The design used in modeling is the circular type (Circular Bearing). As for the products themselves, using Bridgestone. VOLUME 21 │ NUMBER 01 │ JULY 2021 https://ejournal.worldconference.id/index.php/neutron E-ISSN: 2685-3272 | P-ISSN 1412-0860 Table 7. Section Properties HDRB1100 Comparative Results Analysis of elastomeric bearing, Lead Rubber Bearing (LRB) and High Damping Rubber Bearing (HDRB). From the analysis using the CSI BRIDGE program, the comparison results of elastomeric bearing, lead rubber bearing (LRB) and high damping rubber bearing (HDRB) are as follows