Masjid Nurul Iman

The structure was evaluated in the spring of this year as part of a research project by students at Stanford University studying potential tsunami evacuation structures in Padang.  Therefore, pre-earthquake photos and partial existing structural drawings were available for review.

Figure 1. Masjid Nurul Iman, one of the largest mosques in Padang.

Masjid Nurul Iman is one of the largest mosques in Padang, and has tall 6 meter story heights.  The foundation consists of a concrete slab on grade with grade beams and concrete piles.  The primary lateral force resisting system consists of reinforced concrete moment frames, and unreinforced brick masonry infill walls at the first story. The second floor consists of a concrete slab, and the roof is a combination of concrete beams and steel truss dome framing. The following photos were taken before the September 30th earthquake.

Figure 2. Masjid Nurul Iman before the September 30th earthquake.	Figure 3. Structural system: RC moment frames and unreinforced brick masonry infill walls.
Figure 4. Roof is a combination of concrete beams and steel truss dome framing.	Figure 5. The building appeared to have performed well during the September 30th earthquake.

The building appeared to have performed well during the September 30^th earthquake.  There was no visible damage to the main structural system, including the concrete beams and columns, as well as the full-height exterior brick infill walls.  At the first story, there were a few interior brick partition walls which collapsed.  These partial height walls did not extend to the bottom of the second floor, and were attached to the second floor with small concrete columns which could not resist the out-of-plane load induced by the brick wall and appeared to fail in bending.

Figure 6. Walls on the first story did not extend to the bottom of the second floor.		Figure 7. A few interior brick partition walls collapsed at the first story.

Damage at the second story included the out-of-plane partial collapse of some brick balcony walls, the partial collapse of some small full height brick partition walls, and the collapse of about 1/3 of the gypsum board ceiling surrounding the dome.  It is possible that the relatively flexible roof dome diaphragm moved out of phase with the robust concrete structure below, and the differential movement caused the gypsum board ceiling to collapse.

Figure 8. Damage at the second story.	Figure 9. Collapse of the gypsum board ceiling.	Figure 10. Collapse of the gypsum board ceiling.

The Stanford University student group evaluated the expected performance of Masjid Nurul Iman using the nonlinear static procedure (pushover analysis) outlined in ASCE 41.  The analysis was based on a deterministic tsunamigenic earthquake hazard with an estimated PGA of 0.25g (Site Class D).  The resulting pushover curve predicted a transient roof drift of 0.5% and permanent roof drift of 0.1%, which meets the performance requirements for Immediate Occupancy for concrete frame structures.  Strong motion data is not currently available for the September 30^th earthquake, although USGS data estimated the event at MMI intensity VIII.

The mosque has been open since the earthquake, although the prayer area was moved from second floor to the first because of the risk of additional portions of the gypsum board ceiling collapsing.