structural analysis of thule whalebone...

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)

The Structural Analysis of Thule Whalebone Houses 1

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:

a. Strength of bone may very with age, and size.

b. Wood once it has cured is probably more stable?

2) Form – size, and shape in: bone vs. wood


a. Mandibles are curved with a narrowing at the apex

b. 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)

a. Wood can be easily split vs. Bone, which is a different matter.

b. 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)a. Using the description of the pit and approximate location of the

identifiable bones, reconstruct the dwelling.b. Based on this first reconstruction, optimize the placement of major

elements

2) Conduct structural Analysis using Multiframe a. Test 1: Construct and test of the idealized form using only mandibles

b. Test 2: Construct House 4 all mandibles

c. Test 3: Substitute Crania/maxilla assemblies for selected Mandibles

d. 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:

1. Optimal Form - What is the form when guided by an efficient use of material?


2. 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:

a. Lashing

b. Use of ribs as gusset plates

c. Use of ribs to resist hoop stress found in dome like-structures

d. The value of skin covering as a membrane structure

3. Loading conditions

a. What was the impact of dead, (weight of the structure) and live loads

(wind) on the stability of the form? Which were more critical?

b. 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



Shear stress

Deflection


Test 3: Substitute Crania/maxilla assemblies for selected Mandibles

Case1: dead load



Shear stress

Deflection

Compare results from Tests 1-3

Case1: dead load



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


a. Materials i. Unknown properties – lack of good data on Shear modulus and E

ii. Lack of homogeneityb. 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.

2. Structural Analysis as a Testing tool

i. Shows the limits of form

1. Under various loading conditions (live and dead loads)

ii. Reveals the limitations of existing knowledge.

1. Material properties

2. Specific of construction – Construction techniques

a. Lashing

b. Use of ribs as gusset plates

c. The value of skin covering

i. Coefficients of friction, and surface features impacts the ability

to lash elements together to create a frame structure

3. The value of precedent in design

a. Adapting old techniques to a new site context

i. Why use inferior materials in a structural design

1. Ceremonial and culture value

2. 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) wwww.cs.ukc.ac.uk/people/staff/nsr/vrsig.num.

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 2The 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



Shear stress

Deflection

Test 2: Construct and test House 8 version B.

Case1: dead load



Shear stress

Deflection

Test 2: Using results in Paper 1, Compare results test 2 and House 4

Case1: dead load



Shear stress

Deflection

Possible Research Findings

1. Ceremonial vs. the Utilitarian

1. New design approaches may have been developed to accommodate the desire

to integrate Crania/Maxilla elements.

a. Using mandibles to support Crania/maxilla elements

2. Or is this a case of making do. I think it is the former.


structural analysis of thule whalebone...

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