Inspection of structural masonry 6

[Rjeffery]

I am developing a lecture series on the inspection of structural masonry, including bearing walls and CMU retaining walls. I have ACI and NCMA references as well as actual photos, video and Masterspec (generic) specifications and general plans for masonry construction.

I would like to know what else should I empart to my class of professional engineering technicians, geologists and Jr. civil engineers. Is there any things like 'Watch the way they proportion the mortar.' and 'pilasters are a great place to hide lunch trash.'

Thank you in advance for your time and effort.

Rjeffery

 

[haynewp]

I think that not pouring the wall in lifts is done good bit more than we think as workers get in a hurry. I would make that a point.

 

[dik]

Lots of things to look for:

CMU's? Size, Types? strengths? How is strength determined? effective area for design?

mortar? types? reasons for types? testing? absorbant, non-absorbant molds? construction of absorbent molds using CMU's?

Any horizontal reinforcing? the pattern of the horizontal reinforcing? hardness of reinf? deformations? splice lengths? treatment at corners?

Regular rebar at openings? bond beams? rebar around corners? reinforced lintels as compared to steel beams and angles?

bearing issues? slenderness? safety factors?

Lintels? bearing plates? HDG for exterior? coating?

masonry ties? adjustable ties? ties to columns?

mortar joints? types? spacing? thickness? reason for controlling thickness? tooling? reason for various types? raked joints? disadvantages? struck joints (flush)? head joints and special treatment where grout filled?

grout? spec for grout? increase in strength for grout due to absorption into CMU? height for filling? concerns for not complete filling? real or imagined? can you compare a non-filled portion to a wall with a window opening that has been blocked up?

Hot and cold weather masonry?

fastening of objects to masonry? types of fasteners?

just to mention a few...

 

[jheidt2543]

dik has included the laundry list of items that everyone on a masonry job should be aware of. I would like to add one thing your students should be exposed to before going out on a jobsite to inspect masonry - a real mason! Have a local mason contractor come in and talk about all of these things from the standpoint of actually having to do the work. As engineers, we may understand the theory of masonry, we have to wade through codes, specs and calculations, but unless it is all put in a format that can be transmitted to the field it don't mean a thing. The guy that actually has to do the work, whose job is on the line, who living is made laying the block or brick is the one that can really impart the lesson of masonry to your students. It is good to keep in mind that our designs have to be constructable, so let's talk to the guy who has to build them, they are a lot smarter than they get credit for.

 

[Rjeffery]

Thank you,

All great ideas. dik, your list looks alot like my original but with several great thought provoking additions. high and low lift grouting techniques have always been an issue as have been splices in the reinforcing steel, haynewp. Muddy footings, wet CMU, dry brick are also common problems, on site, that a real, honest to goodness mason could offer insights on as jheidt2543 pointed out.

These students are going to be inspecting masonry in construction from footing to roof. Some may go on to design structures or may continue as inspectors in both QC and hopefully QA roles. I hope they will also be able to teach the next 'generation' of young engineers, geologists and technicians.

Thank you guys, again.

 

[jheidt2543]

My comments above were to make the point that students should be exposed to the practical side of construction as well as the theoretical. As we all know, there can be a big difference between what a design looks like on paper and what it looks like close up in the field.

Years ago we were working on a public works project for our city. An assistant city engineer came out to the job site with a T-square to check that the reinforcing steel bends were actually 90 degrees! Our superintendant nearly threw him in the river. Inspectors need to be practical and know what they are looking at. They have to understand the design and the field operations well enough to know what is important to the project's success and what is trivial.

An experianced, professional tradesman is a joy to watch working at his trade. He can give a student or beginning inspector a real jump start on the details of construction, why some things work and others don't. Some of my best learning experiances were from knowledgable tradesmen. And the really good ones enjoy talking about their work.

 

[dik]

Control joints! Case History of failures... temporary bracing... and the list goes on...

 

[CWIC]

Lot's of good technical information has been provided here.

I would like to add a few non-technical issues speaking as a special inspector and as a code enforcement consultant:

1.) Integrity: Special inspectors are notorious for NOT being at the job site, but still sign off paperwork including reports, trip tickets, etc. The excuse of "... I have to cover 2 or 3 jobs per day..." is not a good excuse for not monitoring work in progress which requires special inspection contractually or mandated by the code. Others get the contractor to take grout samples or cylinders on the inspectors' behalf, etc. The term "continuous inspection" is the verbage used in the UBC/IBC. Periodic inspection is another story all together. Worse cases include signing COC's for work that has never been inspected, but the contractor paid to get a field report by someone willing to attest to monitoring the work. I actually have a photo of a special inspector sleeping behind the masonry structure he was supposed to be monitoring. I really dwell on the subjects of integrity and honesty in my SS&W classes.

2.) Documentation: Many inspectors submit "generic" reports noting "...visit to jobsite, observed cells being pumped..." etc. The report is inconclusive and does not specify clear and concise information such as: what time the work was in progress, or time of gouting, ambient temperature, gridlines or elevations, etc. (Was there any vibration to ensure consolidation and complete fill?)

3.) Continuing Education: Upon recept of their card and wall certificate, most inspectors call it quits as far as further training or studying goes. Many trades are evolving quite rapidly with regards to raw materials used, workmanship, techniques and current industry practices. Many often scoff at the idea of attending code update courses, the codes do evolve as well. So do inspection procedures and requirements in addition to the technical advances.

I could go on, but...

 

[nhyankee2]

Information on oversanding of the mortar, retempering and breaking the units with a hammer before and after installation (by other trades) would be an eccellent topic for discussion. On site storage should be talked about.

 

[Ron]

RJeffery...I'll throw in another $0.02.....

Mortar is almost always done poorly! Of the three general mortar types, Type S is most common. When done by proportion specification using mortar cement, it will almost always fail compressive strength comparison tests.

The most common mistake I see in proportioning mortar is the use of shovels to measure the sand. This results in oversanding in the morning when the sand is damp and holds together (and while the mason's helper has less tired muscles!), and undersanding in the afternoon when less sand ends up on the shovel. Same count, different volumes!

To correct this, require that masonry sub use a 1 cubic foot wooden box and measure sand and cement in the box. This way proportions will be a lot closer in consistency.

Next is the sampling and testing....
Many labs use mortar cubes. Some use small cylinders. I am a firm believer that mortar specimens should not be moved to the lab for 48 hours (typical is 24 or less). The strength is relatively low at 24 hours and the potential for sample disturbance is great.

I like the cylinders over cubes because of the more correlative stress distribution, and less potential for sample disturbance.

 

[Tibby]

Drainage for the retaining walls.

 

[Ron]

Rjeffery...one other point I forgot to mention. Head and bed joints. Head joints are rarely filled properly. This creates a potential structural compromise (less vertical shear strength) and a waterproofing issue that can lead to structural concerns.

When serving as the Special Inspector of Record (a Florida quirk!)I require full head and bed joints, not just the outside edge. I also require cleanout of all mortar in cells to be concrete filled (grouted).

 

[boo1]

Truss attachment is one of our common trouble areas.

 

[VoyageofDiscovery]

One more thing, when inspecting reinforced masonry walls, make sure the Contractor isn't pulling up the bars, believe me this happens.

VOD