My love of Egypt and my first contact with Egyptian construction started in 1994 when I was asked to provide a scheme to strengthen parts of historic Cairo after the devastating earthquake in 1992. This initial contract was to work with the state-owned Arab Contractors to strengthen the Al Ghory Mosque, which had been extensively damaged. It was at that time that I was able to visit the Giza Plateau to see the pyramids.


My first view of the Great Pyramid was in the early evening when I got out of my vehicle at a local hotel. I was expecting to see a pyramid, but I was not prepared for the scale and size of the monument that was in deep shadow at that time of the day, almost obliterating half the sky. Like many other visitors, the first question that inevitably came to my mind was: ‘How could people with primitive tools build these fantastic monuments in such a short time?’ At that time, I did not take any professional interest in the construction of the pyramids, but I did feel a great deal of respect for the constructors.


Although we have been fascinated with how the ancient Egyptians built these incredible monuments, there is still a lot of discussion and mystery surrounding the actual method. The Step Pyramid of Djoser, which is 62 meters (203 feet) high, was the first high-rise structure that the ancient Egyptians built; previously, their structures were no more than 10 meters (33 feet) tall. How did the ancient Egyptians manage to construct the Step Pyramid, having never before erected a structure anywhere near that size?


My professional interest in the construction of the pyramids was initially sparked by observations that I made during Cintec’s work restoring the ceiling of the burial chamber of the Step Pyramid. We were called in to restore the ceiling, which was collapsing due to the failure of the timber beam that the ancient Egyptians had used to hold the ceiling stones in place (Figure 1). Our unique Waterwall airbags supported the dangerous hanging stones temporarily, and our patented anchors permanently secured them (Figure 2).


While in the burial chamber, I noticed that although we were drilling holes that were 4 meters (13 feet) in length, we never actually drilled through stones that were more than 40 centimeters (16 inches) wide. This appeared to be a direct contradiction of the common belief that the enormous stones on the outside were the same all the way through the pyramid. In some cases, the fill was a great deal smaller. It was this observation that prompted me to question the accepted theories that attempt to explain how the pyramids were built. Having worked in the construction industry for 54 years, I began to analyze these theories from a practical builder’s perspective.


I put myself in the mind of an ancient Egyptian builder faced with limited tools and little experience of large-scale construction. The main problem that I found with the existing theories was that, from a builder’s perspective, they made the process more difficult than it needed to be. Why would the Egyptians haul huge stones from a long distance away unless it was absolutely necessary? The internal core and filling would never be seen, so why fill it with quarried blocks that took time and presumably money to extract and transport to the site? The logistical problems were already enormous -- coordinating all the elements from quarrying, transport, scaffolding, design, setting out and manpower requirements.


Cintec has undertaken restoration work in both the Red and Step Pyramids in Egypt, and during this work I have observed the progression of the ancient Egyptians’ knowledge of construction techniques. With every pyramid they built, they became more skilled and corrected previous design defects. One such example is their use of corbelling to create openings in the pyramid for the burial chamber.


At the Step Pyramid, the builders attempted to create an opening for the chamber by using large timber beams. However, the timber buckled and failed, causing stones to fall. It was this failure that Cintec was brought in to correct. When the ancient Egyptians moved on to create the burial chamber ceiling in the next two pyramids, the Meidum and Bent Pyramids, they attempted to use a corbelling technique to overcome the failure of the timber beams. Both of these pyramids have unusual shapes; the Bent Pyramid’s top section sits at a slightly different angle to the main body, giving the structure its ‘bent’ appearance, while the Meidum Pyramid has the appearance of a truncated box sticking out of the ground, rather than the even slopes of the later pyramids.


Corbelling stone and masonry is now a well-known technique in construction. However, the ancient Egyptians were newly using it when building the pyramids. Therefore in both the Meidum and Bent Pyramids, the builders exceeded the overhang needed for the corbel arch to support the weight. This resulted in the burial chamber being squeezed together, and it is this mistake which I believe is the cause of both pyramids’ unusual shapes. The builders rectified it in the construction of the next pyramid, the Red (or North) Pyramid, which is a perfect example of the correct use of corbelling and has a true pyramid shape.


This progression of knowledge shows that the ancient Egyptian builders were pragmatists, and as such would have always built in the simplest and most efficient way they knew how. As stated earlier, I have found many of the existing theories on how the pyramids were built to be overly complicated and sometimes entirely impractical. I believe that they instead employed much simpler and therefore more viable methods than many current theories propose. It is my opinion that the pyramids were constructed using internal ramps, combined with some additional scaffolding, and not with enormous external ramps, a theory currently favored by many archaeologists.


I believe that the pyramids consist of three different layers (Figure 3). First is the middle core that is visible on every pyramid after the Bent Pyramid. I predict that this layer is only three blocks wide, with the blocks diminishing in size as they near the apex. This layer was used by the Egyptian builders to retain the core filling and would have been a key to connect the outer cladding. The step design of the pyramid meant that the builders were able to connect the cladding to the pyramid while still supporting the weight of the cladding blocks.


From my observations of the burial chamber of the Step Pyramid, I believe that the infill and central core of the pyramid primarily consist of much smaller stones, and any other larger blocks that the builders wanted to conceal. The inner core was used to create internal ramps, which enabled the Egyptians to build the pyramid from the inside out (Figures 4 and 5). The ramps were started at the mid-point of the pyramid and would zigzag across its full internal width, matching the height of the middle-core stones as the pyramid was built. The small number of heavy middle core blocks could have been raised on these internal ramps and positioned at the perimeter of the pyramid. As most of the inner fill stones were much smaller, they could have been easily handled by men and animals.


The ramps would get steeper as the pyramid grew in height, but they would not exceed the normal angle used to calculate the external ramp gradient. The ramps could have had small palm tree trunks partly embedded into them as a mechanism to slide the heavier core blocks on wooden sledges. As the pyramid reached the apex, more reliance on scaffolding would have been necessary to top out the structure.


The final layer is the outer cladding, which would have been added last and used by the ancient Egyptians to smooth the outer appearance of the pyramid and ensure its ‘true’ pyramid shape using additional stones or tufla grout, like the final icing on a cake.


Some people have been skeptical of any theory involving the use of scaffolding, as they argue that the ancient Egyptians would not have had access to enough timber. My method requires only a small amount of scaffolding in order to attach the outer cladding, and the same scaffolding could have been moved around the pyramid as they worked. In recent restoration work on the pyramids, traditional timber lashed together has been used as scaffolding (Figure 6), which demonstrates that it clearly would have been possible to use scaffolding to construct them in the first place.


I acknowledge that these are only my theories and not facts. However, there is a way to prove my theory of the layers of the pyramid, and I volunteer to carry out this work at no charge to the Egyptian Antiquities. We could diamond drill 100-millimeter (4-inch) core holes into the pyramid at varying heights to a depth of 30 meters (100 feet) and provide a drilling log of all the contents of the bored hole to establish the true nature of the fill. The drilling would be done with the latest dry drilling techniques to prevent damage to the pyramid, and the core would be plugged and filled to match the external appearance.


The short period of intensive construction by an ancient civilization who managed to build these wonderful monuments was remarkable. One can only admire the great ingenuity and effort that was required by a team of specialist builders, who from the very start showed great ingenuity and the ability to adapt, overcome problems, and learn from their mistakes.▪


The Timber Tower Research Project by Skidmore, Owings & Merrill, LLP (SOM) was publically released in June of 2013, and is available for download at SOM’s website. The goal of the research project was to develop a structural system for tall buildings that uses mass timber as the main structural material and minimizes the embodied carbon footprint of the building. The structural system research was applied to a prototypical building based on an existing concrete benchmark for comparison. The concrete benchmark building is the Dewitt-Chestnut Apartments, a 395-foot tall, 42-story building in Chicago designed by SOM and built in 1966.


SOM’s proposed system is the "Concrete Jointed Timber Frame". This system relies primarily on mass timber for the main structural elements, with supplementary reinforced concrete at the highly stressed locations of the structure: the connecting joints. This system plays to the strengths of both materials and allows the structural engineer to apply sound tall building engineering fundamentals. The result is believed to be an efficient structure that could compete with reinforced concrete and structural steel systems, while reducing the embodied carbon footprint of the structure by 60 to 75%.


The basis of the research project was rooted in sustainable urban development. Recent population projections have estimated the current world population of 7.0 billion people to increase to 11.0 billion people by the year 2050. More importantly, the number of people that will be living in cities has been estimated to double from 3.5 billion people to 7.0 billion people in the same time frame. Tall buildings will likely be needed in order to house that many additional people in growing cities. Tall buildings constructed to meet population demands need to be developed in sustainable ways to limit environmental impacts.


Tall buildings built using current technology and materials pose a challenge to sustainable city development because they offer both positive and negative environmental impacts. Positive impacts include reducing urban sprawl, promoting alternative transportation, and efficient energy use. These benefits come at the cost of emitting more carbon dioxide to produce the materials and to construct the building. These carbon emissions are referred to as the embodied carbon footprint of a building. A tall building’s embodied carbon footprint is significantly higher relative to low-rise buildings on a per square foot basis. This is because the structure is usually responsible for the majority of the building’s embodied carbon footprint, and tall buildings require far more structure to support their height. The structural system chosen for a tall building can have a significant impact on the overall embodied carbon footprint of the building.


Structural engineers currently have four primary materials in which to design buildings: steel, concrete, masonry, and wood. Tall buildings currently use steel or concrete almost exclusively, for two reasons. First, with some limited exceptions, non-combustible materials are required by most building codes for buildings greater than four stories tall. Second, steel and concrete have higher material strengths than masonry and wood, making them a natural choice for tall buildings which require support of very large loads. These factors have generally limited wood use to low-rise buildings. Recently, developments in mass timber technology are overcoming these challenges. Mass timber products such as cross-laminated timber (CLT) can be built up using small pieces of dimensional lumber and structural adhesives to achieve panels as large as 1foot thick and 40 feet long. These panels can be used as floors and shear walls with structural sizes necessary to support a tall wooden building. Wood members of this size have an equally important characteristic; they behave like heavy timbers in a fire and form an insulating char layer which protects underlying material. The charring behavior is predictable and preserves a portion of the member’s structural strength, making performance based fire design of mass timber structures possible. Mass timber has made wood a viable choice for multi-story buildings as evidenced by completed projects in Europe and Australia, and many other proposed projects around the globe.


The structural and fire engineering advancements of mass timber have made recent multi-story wood buildings possible. However, the sustainability of wood seems to be an equally important consideration in the resurgence of multi-story timber buildings. Wood has been shown to be more sustainable than other materials because it generally requires less energy to produce compared to structural steel and reinforced concrete. More importantly, wood is approximately 50% carbon by weight, a carbon sink that is the natural result of photosynthesis. These sustainable aspects of wood make mass timber an attractive material from which to construct the sustainable cities of the future. The intersection of increasing urban populations, need for tall buildings, and the sustainability of wood has led to the increasingly popular concept of tall wood buildings. SOM has committed decades of tall building design expertise to furthering this concept, through the Timber Tower Research Project, by identifying key design and construction issues related to tall wood buildings and proposing the "Concrete Jointed Timber Frame" structural system. This system is optimized for tall buildings and could be competitive with existing tall building structural systems. The proposed system balances the requirements of building marketability, economy, and sustainability.


The primary goal of any structural system is to provide a marketable and valuable building to the owner and occupants. A marketable building must have adequate and flexible floor area to layout useful space for the occupants. The most marketable building layout is an open floor plan which allows a variety of room layouts and maximum flexibility for future changes. An open floor layout requires that the floor structure span the entire distance of the leasable area. This distance in the Benchmark Dewitt-Chestnut building was 28 feet 6 inches, with a clear span of 26 feet 3 inches. The most advantageous system to span this distance is a flat mass timber panel which minimizes floor-to-floor height of the building. The required panel thickness to span the required distance was determined to be 13½ inches. This thickness was thought to be too great compared to the material required for the Reinforced Concrete Benchmark to be economically viable. Therefore, alternative methods to span the required distance were investigated in order to reduce the amount of structural materials used.


The controlling design consideration for the mass timber floors was determined to be vibration due to occupant activity. The floors were analyzed according to American Institute of Steel Construction Design Guide 11, utilizing the velocity-based methodology, which was found to be more useful for flat slab-type floors. Evaluation of the criteria shows that increasing floor stiffness is the most effective way to control vibrations. The floor stiffening effect of end rotation restraint (fixed end condition) was quickly realized as an efficient way to reduce vibrations. It was determined that an 8-inch-thick mass timber floor panel could be used if end restraint was provided. This requires moment connections at the intersection of mass timber floor panels with vertical elements such as mass timber shear walls and structural glued laminated timber perimeter columns. Several connection schemes were investigated to provide the required moment connections. Steel reinforcing epoxy connected to the mass timber and cast-in reinforced concrete joints were determined to be the most reasonable solutions due to the ability of reinforced concrete to resist complex load paths. These reinforced concrete joints are able to resist floor-to-floor compression, shear, bending moments, and torsion, thus creating an efficient composite-timber system.


The reinforced concrete joints also proved to be useful in other tall building aspects. The concrete jointing between timber floors and timber shear walls provides a link beam between individual wall panels. This creates a stiff lateral load resisting system which is required for a tall building. It was also determined that the demands on the link beams were beyond the capacity of a structural glued laminated wooden link beam, requiring the use of a material other than wood. The concrete joints and link beams were also useful in the design of the lateral system to resist net uplift due to lateral loads. The Prototypical Building has approximately 40% of the dead load of the Benchmark Building. This led to net uplift forces at the extremities of the lateral load resisting system. This net uplift would have been exacerbated without the concrete joints which account for over 50% of the entire structure dead load, yet only 20% of the structural material volume for a typical floor.


A comparison of the structural materials required to construct the Benchmark and Prototypical building shows that the proposed system is very efficient in material consumption and could be competitive with reinforced concrete. The goal of minimizing the structural materials used, namely mass timber, will help reduce costs and minimize new demands on forest resources which may become strained due to increasing populations and demands.


The non-structural effects of the proposed system were evaluated and the most notable effect was the acoustic treatment required on top of the mass timber floors in order to achieve a marketable acoustic rating. The most effective treatment was determined to be a 2-inch-thick gypsum concrete topping. This treatment thickness, in addition to potential ceiling finishes, required 3 inches of additional floor-to-floor height in order to maintain the same floor-to-ceiling height as the Benchmark building. This has impacts on wind loads on the building, and non-structural costs such as the exterior wall system.


SOM believes that the proposed system is technically feasible from the standpoint of structural engineering, architecture, interior layouts, and building services. Additional research and physical testing is necessary to verify the actual performance of the structural system relative to the theoretical behavior. SOM has also developed the system with consideration for constructability, cost, and fire protection. Reviews from experts in these fields, and physical testing related to fire, is also required before this system can be fully implemented in the market. Lastly, the design community must continue to work creatively with forward thinking municipalities and code officials using the latest in fire engineering and performance based design to make timber buildings a viable alternative for more sustainable tall buildings.▪