Tacloban Charity Project: London Update

For the past nine months Philippe and I have been offering technical engineering support for the design of the dormitory structure in Tagpuro in the aftermath of super-Typhoon Yolanda. For more information on the project visit our previous blog post here and the Workshop blog here.

Prior to Typhoon Yolanda, the local design code stated a wind speed of 250kph should be modelled. Yolanda created wind speeds of 320kph over prolonged periods of time, meaning the codes became outdated. When you have such high wind speeds it’s really important to understand how it is likely to behave around a structure. The protruding rafters of the dorm block create chaotic wind behaviour which is best modelled using a wind tunnel or Computational Flow Dynamics (CFD).  We worked in conjunction with Chris Ochyra, an expert in Advanced Engineering from Ramboll’s Southampton office, to model the wind around our four buildings. It’s important to account for the topography and land features in the local geographical area which means the CFD boundary conditions are critical. The ANSYS CFD model outputted values for the pressure coefficient (Cp) which we converted to member and area loads and applied to the global structural SAP model. We modelled the structure with and without louvre panels which allowed us to understand whether it would be best to open or close these removable panels during high-wind scenarios.

We found that the lead engineering practice (based in Manila) underestimated the loadings upon several key areas and we hence undertook a thorough review of structural members. This highlights the importance of using CFD for analysis because the values they had taken from literature were far too low and members could have failed during high winds.

The Philippines and Tagpuro is also susceptible to earthquake and is therefore important to ensure the building behaves well under seismic loadings. A seismic review was carried out in coordination with Davide Pedicone. Davide has worked extensively on the seismic rebuilding after the 2009 L’Aquila earthquake in Northern Italy and in California. His experience has been invaluable for this project.

In the dormitory building, the three large concrete cores provide the building’s stiffness and strength. In between the cores the building is based on a series of timber frames, rafters and purlins. The loads generated from their seismic mass will be transferred through to the cores and down to the foundations.

The results from the seismic model highlighted some of our concerns about lateral drifts (in excess of 150mm!) and the adequacy of the design of the bracing. The bracing is provided by large timber cross beams in the transverse direction and by the purlins in the roof. In light of our seismic study we have recommended additional diagonal steel bracing rods connecting the roof to the core which will limit drift to an acceptable level (8mm). In seismic design, members are designed beyond their elastic limit during large earthquakes. The result is some plastic deformation and damage such as cracking. The timber cross bracing was designed fully elastically to avoid a loss of strength or stiffness and so maintain the integrity of the building in an earthquake. In earthquakes it is also important to design for redundancy, or in other words the loss of key members.

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Tacloban Charity Project: Work Experience Student Takeover

Myself and three other work experience students were part of the Ramboll Structures Department in London for one week from 29th June. One of the projects we worked on was the Tacloban project, one of the charity projects Ramboll supports. Ramboll is currently working on this project alongside a local architect and engineering practice in Tacloban.

 

 

 

Tacloban is the capital of Leyte, Philippines. 360 miles southeast of Manilla, it has a population of 221,174 and is the most populous city. Typhoon Haiyan (2013) was very destructive and claimed the lives of 10,000 and affected about 11 million. With wind speeds of roughly 310km/h (195mph) many homes, schools and the airport were severely damaged. The following storm surge was reported to have reached up to 5m and when combined with the low lying land of Tacloban (the airport being some 5m below sea level) the results were disastrous.

The chances of a similar disaster occurring are very high, as the Philippines is located in a disaster hotspot and has many hazards, such as typhoons due to the warm ocean water, high humidity and low atmospheric stability.

The Tacloban charity project consists of 4 buildings which must be designed to withstand a similar disaster and provide a shelter, education and a clinic to the people who live there. However, the design process is not easy as there are various constraints with regards to the area. Firstly, Tacloban is extremely prone to hurricanes and typhoons. These involve winds of up to 320 km/h. One can see how this factor makes the designing and building of these structures difficult, as not only must the buildings be made to resist such high speed winds when complete, but they must withstand the conditions during construction too. In order to accommodate these high pressures, Ramboll has used features such as a hip-roof that is ideal in hurricane-prone areas. This is ahiproof roof where all sides slope down to the walls with gentle slopes, increasing its ability to withstand high winds as there are fewer sharp angles.

Another constraint faced is the lack of roads in the area. Tacloban is a rural area that is very poorly developed so does not have main roads. This make the transport of construction materials difficult as the required large vehicles cannot travel on the current dirt roads. Hence new infrastructure within the local area must also be developed.During my work experience at Ramboll, I have made detailed models of the structures that are going to be built to aid as many people as possible by providing them with healthcare, shelter and an education.

study centre model   foundation plan study centre

The other work experience students and I initially looked at the plans of both the study centre and the clinic. We then worked out the effective areas of the columns in the structure and calculated the load exerted on each column, using load values provided in the code.This data will then be used to design the timber perimeter columns.

Following this process of calculating loads, we moved on to look at the wind pressures exerted on the faces of the buildings. We used the pressure coefficients and the wind models created for us, along with Bernoulli’s equation, to find out the average maximum and minimum pressure exerted on each face of the building. This information was then added to the digital model and used to ensure that the building was strong enough in these certain areas. Working with the structures team and the other work experience students on this project was thoroughly enjoyable and gave us a true insight into the world of engineering.