principles of joints & sealants chapter 9. mehta, scarborough, and armpriest : building...

Principles of Joints & Sealants

Chapter 9

Mehta, Scarborough, and Armpriest : Building Construction: Principles, Materials, and Systems

© 2008 Pearson Education, Upper Saddle River, NJ 07458. All Rights Reserved.

Joint patterns & details



Building Joints result from need to

Work with materials that can be easily fabricated, transported and assembled on site

Allow for field adjustments Accommodate differing changes in size

between different materials Make a secure connection Articulate building surfaces



Types of joints

Static joints provide non-moving connection between building components

Dynamic joints (Movement Joints) make connections while allowing for movement of the components



Building separation joints

Continuous joints that completely separate parts of a building from each other

Accommodates effects of movements of building as a whole

Prevent stresses created in one part of a building from transferring to other parts.

Typically1 1/2 inch - 2 inch wide, every 250 ft.



Typical locations of building separation joints



Two adjacent columns at separation



Building separation: double columns in concrete frame



Building separation: double columns in steel frame



Building separation at single column



Seismic Joint

Assure that one building segment does not collide with another during an earthquake

Accommodate mostly horizontal movement Typically wider than a building separation

joint, with width increasing with height



Typical seismic or separation joint cover



Factors in sizing movement joints

Thermal movement Moisture movement Elastic deformation and creep Construction tolerances Sealant (if used)



Restrained & unrestrained joints



Thermal movement

Occurs in all components Generally most critical type of movement Coefficient of Thermal Expansion (), property of a

material

t (change in length) = L (t)

t is a function of Annual temperature range Temperature at the time of construction



Approximate value for selected materials



Northern US: typical temperature gradient



Southern US: typical temperature gradient



Problem: Determine joint width between 100 ft.

segments of brick masonry wall

t (minimum joint width) = L (t) L = 100 ft = 1,200 int = 80ºF = 4.0 x 10-6

minimum joint width = (4.0 x 10-6)(1,200)80 = .320 in



Moisture movement

Some materials expand on absorption of water or water vapor In some materials (brick), expansion is permanent Some materials return to original shape when

dried



Elastic deformation & creep

Creep is incremental deformation of a component caused by sustained loading.

Significant in concrete and masonry



Connection between spandrel beam and non-loadbearing infill wall must account for deflection



Tolerances

Material tolerances are the allowable variation in size from unit to unit

Construction tolerances are a function of quality control during construction. Small tolerances require good construction quality and supervision

Other tolerances include foundation settlement, story drift, chemical processes and freeze-thaw



Total joint dimension

Width of Joint

Width based on temperature, moisture and other movement + Tolerances=



Joint sealants

If a joint sealant is used, its movement ability must also be considered

Joint sealants are categorized by movement ability (class 50 has +/- 50% movement ability

Width of Sealed Joint

Width based on temperature, moisture and other movement

+ Tolerances= 100 Sealant Class



Detailing movement joints

Expansion joints Control (shrinkage) joints



Brick expands over time - expansion joint required



Concrete masonry shrinks over time - Control joint required



Components of a sealed joint

Substrate Primer

Improve adhesion of sealant to substrate

Sealant back-up (backer rod) control depth and shape of sealant allows for tooling sealant

Bond breaker Prevents adhesion where not required



Untooled and tooled joints



Effect of bond breaker on sealed joints



Joint sealants

Preformed tapes Perform as sealants only when under pressure

Caulks First generation sealants, dough-like materials, rarely used

Elastomeric sealants Synthetic polymers, most commonly used in construction Vary in performance characteristics

Movement ability Water vapor permeability Abrasion resistance Chemical resistance Durability Substrate compatibility Paintability

principles of joints & sealants chapter 9. mehta, scarborough, and armpriest : building...

Documents

building construction

pearson education

upper saddle river

separation slide

different materials

single column slide

concrete frame slide

steel frame slide