WEEK FOUR
Topic: Construction of Arches: Tudor, Equilateral gothic, Lancet and Parabolic.
Content:
(i) Construction of tudor, equilateral gothic, lancet and parabolic arches respectively.
1. Tudor:
Method of construction: To construct a tudor arch when given the span.
Draw a line AB equal in length to the given span.
Divide AB into 4 equal parts.
Construct a square on the length between the 1st and 3rd divisions ie FPOE.
Draw the diagonals of the square which form common normal to the curves that trace out arch. ie with F as centre and radius FA, draw an arc AM. Then with O as centre and radius OM, draw arc MV. Repeat same with centre P and E respectively to complete the arch.
2. Equilateral Gothic: As the name implies, it is an arch formed by two slant sides of an equilateral triangle.
Method of construction: To construct an equilateral gothic arch when given the span AB.
Draw a line AB equal in length to the given span.
With A as centre and radius AB, draw an arc on the slant side AC.
With B as centre and radius BA, draw an arc on the slant side BC to meet the former arc at point C.
3. Lancet: Lancet arch is similar to equilateral gothic in construction except that it tapers more at the crown than
equilateral gothic.
Method of construction: To construct a lancet arch when given the span AB and rise (height) R.
Draw a line AB equal in length to the given span.
Extend line AB to point D by an amount equal to R/2 .
Extend line BA to point E by an amount equal to R/2 .
With E as centre and radius EB, draw an arc.
Similarly, with D as centre and radius DA, draw another arc to intersect the previous one at point C. The arc produced is lancet.
4. Parabolic: Parabolic arches have the shape of parabolas. Construction method (WEEK 4 of 3RD TERM SS1)
General evaluations
1. Construct a Tudor whose span is 80.
2. Construct a lancet arch whose span and rise are respectively 50 and 40.
3. Sketch 5 types of arches.
Reading assignment
1. Technical drawing by J.N Green page 133.
2. Use www.google.com to search for types of arches
Weekend Assignment
Objective
1. The highest point of an arch is called A. peak. B. apex. C. crown. D. head.
2. Which of the following is not a type of arch? A. Spiral. B. Segmental. C. Semi-elliptical. D. Semi-circular.
3. Which of the following cannot be used in a window opening? A. Arch. B. Lintel. C. Column. D. Beam.
4. The inner wall of an arch is called A. extrados. B. intrados. C. abutment. D. rise.
5. The vertical height of an arch is called A. keystone. B. rise. C. crown. D. run.
Theory
1. Draw and label a typical structure of a semi-circular arch.
2. Sketch the following arches (a) equilateral gothic. (b) semi-elliptical.