The Structural Analysis of a Thule Whalebone House (House4)
Papers 1: (This paper introduces the use of structural analysis as a tool for analyzing and reconstructing House 4.This paper also establishes a foundation for a second paper which will compare the results of House 4 and 8.)
Preface
One criticism of computer modeling is that they often suggest a high degree of knowledge of the structure or site, even though the 3D computer model might represent only one of several possible outcomes. In particular, photo realistic 3D computer models have been criticized because they often do not reveal where information is lacking and where artistic license has been taken to produce a visually satisfying product (Miller and Richards 1994, Ryan 1996, Roberts and Ryan 1997). This paper will reveal the benefits a 3D modeling as a tool for testing several hypotheses will be examined. In this research, a case study a 3D model of a Thule whalebone house (House #4) was constructed from existing archaeological data. In using structural analysis techniques it is then possible to test and evaluate the efficiency and stability of each reconstruction. Using this approach to 3D modeling it is possible to consider:
1)What were there possible arrangements of structural elements?
2)How does each form respond to dead and live loads?
3)Are there any significant construction issues associated with each potential reconstruction?
Testing each case can help inform the actual process of reconstruction. If we consider the different stages of the design process, the analysis stage in reality is often the construction phase: (Note: Italics – Thule whalebone case)
1)Context (Thule: Building with whalebone in a cold harsh climate using only simple tools made from stone and bone)
2)Problem Identification (enclosure of a space heated by whale oil lamps)
3)Possible Design solutions - rule of thumb, precedent serve as a guide (Thule: knowledge of basic frame structures built in wood)
4)Analysis (Thule: Analysis can be conducted using frame analysis today, which was not possible until recently)
5)Construction ( Thule: For these early builders of these structures, the design, analysis test, and construction was conducted on site as a single task).
6)Real world test (Thule: does it stand up in the real world – sometimes steps 4 and 5 are the same for vernacular structures from the past)
7)If design fails start again (step 1: Context) – The passing of time will often reveal problems in the design of a structure. (Thule: For example, a heavy snow loading may reveal the need to add ribs as a means of offsetting hoop stress in the frame).
For architects and engineers of the past, precedent and rule of thumb provided a starting point for the creation of a design solution. If the context did not vary significantly from previous environments, then a design solution would be easily achieved. Existing solutions could be replicated without little change from previous and existing designs. In these cases knowledge preserved through a craft tradition would serve the designer well. However, in cases where, there was a new constraint or requirement; for example, the lack of good building materials, the designer creativity would certainly be tested. For example, when the migration of Inuit across the North in the 9-15th century (check century) forced these early settlers to later substitute whale bone for spruce logs, a new building form unlike early precedent would have to be created. In satisfying a basic need for housing, these designers of Thule whalebone houses would have benefited from working in wood. Using a substitute, whalebone with different properties, would have tested the creative energies of these early peoples. Consider the issues in transitioning from wood to whalebone. A basic understanding of physics from creating sod houses would have provided a crude if not basic understanding of structural principles. Applying this knowledge to world absent of wood would have been a challenge for these early architects.
1)Material Strength – Shear, Bending in: bone vs. wood differs. Adding to complexity of this problem:
- Strength of bone may very with age, and size.
- Wood once it has cured is probably more stable?
2)Form – size, and shape in: bone vs. wood
- Mandibles are curved with a narrowing at the apex
- Wood logs are linear with a narrowing at the apex.
3)Construction techniques using simple bone, stone and wood tools (Peter do you have references to tools used in building these structures)
- Wood can be easily split vs. Bone, which is a different matter.
- Wood vs. bone - Different coefficients of friction, and surface features would impact the ability to lash elements together to create a frame structure.
Methodology
One product of the Thule culture was the construction of unique whalebone houses built from the skeletons of baleen whales. From the excavation of archaeological sites in the Arctic we can ascertain the numbers and approximate sizes of the bones used at each site. Also know was the approximate location of these structural elements that surrounded a subterranean pit that delineated the exterior edge of these houses.
Reconstruction Process
1)Plot Plans (Dawson 1997)
- Using the description of the pit and approximate location of the identifiable bones, reconstruct the dwelling.
- Based on this first reconstruction, optimize the placement of major elements
2)Conduct structural Analysis using Multiframe
- Test 1: Construct and test of the idealized form using only mandibles
- Test 2: Construct House 4 all mandibles
- Test 3: Substitute Crania/maxilla assemblies for selected Mandibles
- Compare results from Tests 1-3
II. Design Issues:
Given that we know these structures stood, even a crude test may help us refine our ideas about the use of materials, and may answer questions:
- Optimal Form - What is the form when guided by an efficient use of material?
- Connections - How did the change of materials (wood to bone) influence the use of connections? How did this change influence the use of ribs in these structures:
- Lashing
- Use of ribs as gusset plates
- Use of ribs to resist hoop stress found in dome like-structures
- The value of skin covering as a membrane structure
- Loading conditions
- What was the impact of dead, (weight of the structure) and live loads (wind) on the stability of the form? Which were more critical?
- How much variance was there in loading. (Wet vs. dry sod). What was the impact of snow loads and drifting on structural stability?
The process of construction:
Outline of the actual process and outcomes from the experiment
Test 1: Construct and test of the idealized form using only mandibles
Case1: dead load
Case2: dead and live load combined
Bending moment stress
Shear stress
Deflection
Test 2: Construct House 4 (all mandibles)
Case1: dead load
Case2: dead and live load combined
Bending moment stress
Shear stress
Deflection
Test 3: Substitute Crania/maxilla assemblies for selected Mandibles
Case1: dead load
Case2: dead and live load combined
Bending moment stress
Shear stress
Deflection
Compare results from Tests 1-3
Case1: dead load
Case2: dead and live load combined
Bending moment stress
Shear stress
Deflection
Research Limitations
In this paper, the authors will consider how the use of structural analysis techniques can be employed to evaluate reconstruction efforts in archaeology. More importantly, can modern structural analysis techniques be used to assist in the reconstruction and interpretation of these early house forms?
First, this approximate location of these elements leaves some doubt concerning how these structures were actually assembled. Small differences in the placement of mandibles, the major structural element can have a direct impact on the structural stability.
Specifically, can the use of frame analysis applications commonly used in the design of steel, concrete and wood structures inform the process of reconstruction a Thule Whalebone house. The paper will consider factors that constrained the design of these structures:
I. Strength of materials:
1)Issues in applying applications designed for common architectural engineering structures to vernacular forms of the past
- Materials
- Unknown properties – lack of good data on Shear modulus and E
- Lack of homogeneity
- Members – Non uniform cross-sections
Connections – Pinned, fixed or spring
Lessons Learned
This paper will hopefully show, how computer modeling can go beyond a mere 3D virtual representation.
- Structural Analysis as a Testing tool
- Shows the limits of form
- Under various loading conditions (live and dead loads)
- Reveals the limitations of existing knowledge.
- Material properties
- Specific of construction – Construction techniques
- Lashing
- Use of ribs as gusset plates
- The value of skin covering
- Coefficients of friction, and surface features impacts the ability to lash elements together to create a frame structure
- The value of precedent in design
- Adapting old techniques to a new site context
- Why use inferior materials in a structural design
- Ceremonial and culture value
- Lack of material
References
Paul Miller and Julian Richards, “The Good, The Bad and Downright Misleading: Archaeological adoption of Computer Visualization, Computer Applications & Quantitative Methods in Archaeology, Tempvs Reparvm, CAA, (1994) 249-254.
J.C. Roberts and N. Ryan, Alternative Archaeological Representations within Virtual Worlds,VISIG97 (1997) w
N. Ryan, Computer Based Visualization of the Past: Technical ‘Realism’ and Historical Credibility in British Museum Occasional Papers, London England: The British Museum, 114 (1996) 95-108.
Paper 2
The use of Structural Analysis as a tool in the evaluation of Thule Whalebone Houses, “Identifying Non-Utilitarian Uses of Whalebone in Thule Inuit Architecture Using Computer Modeling.”
Based in part of “Identifying Non-Utilitarian Uses of Whalebone in Thule Inuit Architecture Using Computer Modeling.” (CAA 06).
Introduction
Archaeologists have long suspected that that the roof frames of whalebone built by Thule peoples were designed to balance two tendencies: the need to construct stable structures, and the desire to communicate important symbolic information to their occupants. In this paper, we look for examples of non-utilitarian uses of whalebone using computer reconstructions of two Thule semi-subterranean houses recorded on Bathurst Island, Nunavut. In this research a 3D computer model was constructed from existing archaeological data. Using structural analysis techniques it was then possible to test the efficiency and stability of different houses forms found in the Canadian High Arctic (ca AD 1000-1600.) Taking this approach possible design solutions can be tested in a virtual laboratory using techniques usually reserved for the engineering of buildings. One advantage of this approach is the ability to differentiate structural from ceremonial uses of whalebone elements in Thule house design.
Methodology
The actual virtual building and tested follows a process first outlined in previous research (see published article Paper#1). In this research the authors have demonstrated the value of structural analysis techniques on idealized and actual house forms built from baleen whales.
The process of virtual construction and testing:
Outline of the actual process and outcomes from the experiment
Test 1: Construct and test House 8 version A.
Case1: dead load
Case2: dead and live load combined
Bending moment stress
Shear stress
Deflection
Test 2: Construct and test House 8 version B.
Case1: dead load
Case2: dead and live load combined
Bending moment stress
Shear stress
Deflection
Test 2: Using results in Paper 1, Compare results test 2 and House 4
Case1: dead load
Case2: dead and live load combined
Bending moment stress
Shear stress
Deflection
Possible Research Findings
1. Ceremonial vs. the Utilitarian
- New design approaches may have been developed to accommodate the desire to integrate Crania/Maxilla elements.
- Using mandibles to support Crania/maxilla elements
- Or is this a case of making do. I think it is the former.
1
The Structural Analysis of Thule Whalebone Houses