Day 21: Wednesday 28 September - Application of the Seismic Evaluation and Retrofit Manual to Delmas 19

The MTPTC's Seismic Evaluation and Retrofit Manual ‘provides criteria for undamaged or repaired building to evaluate their capacity to resist future earthquakes’.

Regan Potangaroa provided me with 7 conditions from the manual that the buildings must meet for the manual to be applicable. Buildings that do not meet all of the conditions must be subject to a building-by-building construction approach.

In this analysis I applied 6 of the 7 conditions to building datasets representing Delmas 19. The datasets were dervied from the cadastral survey and the Lidar imagery.

Condition 1: must be more than 2m away from a canal or water course

66 buildings (13%) are within 2m of a canal so are not compliant.
Condition 2: must have a slope less than 10 percent

A slope map was produced from the Lidar dataset (note: this has not yet been validated).
183 building plots (37%) contain slopes more than 10 percent so are not compliant. These are clustered around the edge of the site.
Condition 3: must have 3-storeys or less

Buildings must have 3-storeys or less. The number of storeys for each building plot was extracted from both the enumeration survey and the BRC ’s verification survey.
Only 1 building plot (<1%) has more than 3-storeys and so are not compliant.

Condition 4: must be more than its heights-distance away from the top or bottom of a bank or retaining wall

This condition was not measurable using the datasets available. There are not known to be many banks within the target area so it may be assumed that most building plots would meet this condition.

Condition 5: must have a height less than 3 times its width or length

To meet this condition the building must have a height less than 3-times its width or length. The height was extracted from a Surface Elevation Model developed from the Lidar dataset. The width and the length were automatically calculated using the SAGESS-derived polygons. The height and the length were then compared.

All buildings complied with this condition.
Condition 6: must have average floor height less than 3.00m (1-storey), 2.88m (2-storey) and 2.83m (3-storey)

The average floor height must be less than 3.00m (1-storey), 2.88m (2-storey) and 2.83m (3-storey). This was calculated by dividing the building height (from Lidar) by the number of storeys (from enumeration verification field surveys).

315 building (63%) do not comply with this condition.

Condition 7: more than 60mm from neighbouring buildings

There must be more than 60mm between neighbouring buildings. If a polygon was found to be adjacent to another polygon in the GIS it is assumed that the gap between the buildings is less than 60mm. Isolated buildings are assumed to meet this condition.

476 (96%) building plots are adjacent to another building and so are not compliant.
Buildings that meet all 7 conditions

Only 3 buildings were compliant with all 7 conditions.

Number of conditions met

The following figure shows the number of conditions met by each building plot. The majority of buildings in the centre of Delmas 19 met 4 or 5 of the 7 conditions.
Summary

The results seem to suggest that the 'Seismic Evaluation and Retrofit Manual' is not applicable to almost all buildings in Delmas 19. This suggests that MTPTC need to consider altering the manual to make it applicable to slum settlements in Port-au-Prince. The results have been passed onto staff at MTPTC.

96% of houses failed the 7th criteria as they are attached to another building.

The accuracy of the Lidar data has not yet been validated. The results from this analysis are therefore only meant to provide guidance.