Kharpocho Fort: A Construction Marvel with Lessons for Eternal Longevity of Structures
By Dr. Rizwan Karim (PhD)
In 16th century when Ali Sher Khan Anchan gave orders to build a strong defensive fort, Kharpocho fort – the king of forts – he very likely didn’t envisage it standing tall and strong after centuries. Kharpocho fort overlooking Skardu city (Figure 1) is a popular tourist attraction now a days. It is situated at an impressive elevation of 7310 feet above sea level. The fort was built to defend against Tibetan and Mughal empire, the two superpowers at the time. Kharpocho fort with its unique architectural and structural features is a marvel that was well advanced of the existing building design knowledge of that time. The original intent was to have it as a bastion of defense, the ancient wisdom also ensured its long-term structural stability and strength. The fort is located in a region which has always seen high seismic (earthquake) activity. It is hard to decipher whether the people who build this massive structure fully understood the science behind the seismic forces and the behavior of structure under seismic activity, however, it is safe to say that the structural material and the structural arrangement they have used has proven to be effective against this strong force of nature; evident by the centuries this structure has survived.
Figure 1: Location of Kharpocho fort on Google Map (River Indus can also be seen in the picture)
Earthquake forces are measured in terms of peak ground acceleration (PGA). Based on PGA, Pakistan is divided into five seismic zones namely: Zone 1, Zone 2A, Zone 2B, Zone C, and Zone D – ranking from the lowest PGA to the highest PGA. Kharpocho fort falls in Zone C, where the PGA can range from 0.24g to 0.32g; g refers to the gravitational acceleration. These gravitational acceleration ranges corresponds to intensity VII on European Macroseismic Scale (EMS-98). In intensity VII, 28% of the buildings in that particular seismic area will be damaged. This signifies the high seismic zone that this fort is located in, and the scale of forces that this structure has seen over the years. The integrity of this fort despite facing such high forces repeatedly over the centuries can be attributed to the unique structural arrangement of timber elements in the large solid stone walls of this fort (Figure 2).
Figure 2: Timber and stone arranged in Kharpocho Fort (Dhajji Dhewari Technique)
Timber as a structural material provides ductility, the ability to bend without losing significant load carrying capacity, to the overall structure. Under earthquake forces, buildings tend to sway laterally (horizontally – perpendicular to their heights) and there is a need for them to be able to do that without failure of the materials. The stone arrangement without any timber will undergo a significant damage after a small lateral deflection but timber members installed in the stone walls provide additional ductility. The timber in the wall allow these walls to deflect farther without significant damage to the overall wall structure. Apart from the inherent ability of the timber members, the arrangement of these timber members in these thick walls is also highly important. The unique structural system used in this fort is known as Dhajji Dhewari.
Dhajji Dewari is a classical construction technique prevalent in the north of India and Pakistan (Figure 3). The word Dhajji originates from persian and is used for quilt patchwork. Similar to a quilt, there is an arrangement of wooden members in small square, rectangular, and triangular shapes in the walls. The spaces in between these connected timber elements are filled with large stones and grout from locally available material. The structure of Kharpocho fort uses the same techniques with wooden members running full height in small square and rectangular shapes. These elements are especially visible at the corners where two walls are meeting each other. The wooden lintels for the openings, in some cases, extend out and form part of the timber system in the wall. This unique arrangement allows for relatively higher lateral deflection in the wall thus performing better under seismic loadings.
Figure 3: Dhajji Dhewari technique used in the walls of Kharpocho Fort
The Kharpocho fort along with other forts and historical buildings in Pakistan embody a unique ancient wisdom that need to be understood better by modern structural engineers. The better understanding can then help preserv these important pieces of history e and the reclaimed use of these structure can help generate further opportunities for income generation through tourism. The preservation efforts need to be in two steps, the first step will beunderstanding the current structure and the extense of damage to the existing structures, as exposure to environmental elements damages the material in the structure thus compromising the overall integrity of structures. The second step will be to work on rehabilitation and reclaimed use of these structures. The rehabilitation efforts need to be very intentional to make it complementary to the existing structure and preserve both the historical look and integrity of structure. Kharpocho fort itself is a great example of such efforts performed by the collaboration of Aga Khan Cultural Service, Pakistan. The fort along with other lesser known forts in the region represent the unique history and construction wisdom, which still needs to be understood and preserved to both preserve the history and ancient structural design wisdom.
