Fernando S. Fonseca

Tensile Strength of Varied-Angle Mortise and Tenon Connections in Timber Frames

AbstractThe tensile strength of varied-angle mortise and tenon connections in timber frames is discussed in this paper. Twelve full-size mortise and tenon connections (four 90°, four 67.5°, and four 45°) were tested under monotonic tensile loading. Initial yield modes observed during testing included peg bending, peg shear, tenon tear out, and mortise splitting. Decreased connection angle corresponded to equal or increased tensile strength but decreased ductility. A theoretical method to calculate the tensile strength of mortise and tenon connections is also developed. The method uses a modified set of yield-limit equations supplemented with local-stress-effect (mortise splitting and row tear out) equations to predict tensile strength. The governing theoretical yield modes agree well with yield modes observed during testing. The theoretical tensile strength is reasonably accurate, averaging 14% higher to 9% lower compared with test results. The findings indicate that mortise and tenon connections are sign...

Properties of Mortar Using Cubes, Prism Halves, and Cylinder Specimens

The compressive strength of quasi-brittle materials, such as mortar, is affected by the shape and size of specimens tested. The Brazilian standards recently changed the method and the shape of the specimens used to determine the strength of mortar. An experimental program was devised to determine the relationship of mortar properties obtained from testing the old shape (prism halves or cube) and the new shape (cylinder) specimens. Mortar batches were prepared with a lime-cement ratio from 0.25 to 3 and a sand-cement ratio from 2 to 12. Both fresh and hardened mortar properties were determined. The analysis of the results yielded correlations between the strengths of the different specimens. For mortar strength between 4 and 12 MPa (580 and 1740 psi), the strength of cylindrical specimens was 30% lower than that of prism halves specimens; for mortar strength less than 4 MPa (580 psi), the reduction varied from 37 to 49%; while for mortar strength greater than 12 MPa (1740 psi), the reduction varied from 1 to 26%. A relationship was also developed to help engineers proportion mortar based on different percentages of lime and sand.

Relationship between the Compressive Strength of Concrete Masonry and the Compressive Strength of Concrete Masonry Units

AbstractThe results of axial compression tests on masonry prisms can be the basis for determining the design capacity of masonry elements since several building codes permit the compressive strength of the masonry to be that of the prisms. The cost and time required to construct and cure the prisms and the cost and time to prepare and test the prisms, in addition to the waiting time to begin construction, makes the overall prism test method expensive. Building codes, therefore, often provide an alternative to the prism test method. Typically, the alternative method establishes the compressive strength of the masonry from the compressive strength of the masonry unit and the mortar type specified by the engineer. The study presented herein is related specifically to concrete masonry, and it determined a relationship between the compressive strength of ungrouted and grouted masonry and the compressive strength of the masonry units. The relationship was established statistically using the results of a compreh...

The Sobrado Vallim Rehabilitation Project

This paper presents the assessment of the historical two story Sobrado Vallim building located in Bananal, in the state of Sao Paulo, Brazil. The Sobrado Vallim was built as the house of the local coffee Baron. Since being unoccupied by the family, the building has served as a school and as the City Hall; more recently the building has housed a local community association. The first story is formed by rammed earth walls supporting a wood floor. The walls on the second floor are built with adobe blocks, and several wood columns embedded into the walls support the wood roof trusses. The building has been unoccupied for several years and a temporary shoring system has been designed and installed to prevent possible collapse. The analyses included measuring and defining the building structural elements to determine their capacity. The rammed earth walls compression strength was determined using flatjacks. Samples of the adobe blocks were obtained so that their physical and mechanical properties could be determined through laboratory testing. Thermography was used to assess the wood elements condition. The proposed structural solution was to maintain the shell of the building and construct a steel frame structure within the existing elements. The steel frame would reduce the span and partially support the roof trusses at their mid-length. The ends of the wood trusses would still bear on the existing second floor walls. The proposed solution reduced significantly the loads on the existing elements, allowing the form the building to be maintained.

A Proposed Test to Evaluate Efflorescence Potential of Ceramic Blocks

Masonry is susceptible to efflorescence, which in itself is an aesthetic problem, but the condition of efflorescence indicates that water is moving through the masonry in unintended ways and the presence of uncontrolled water can lead to serious issues, including structural problems. In this paper, the results obtained from a proposed test method to evaluate the potential of efflorescence of ceramic blocks are compared to that obtained using the method described in ASTM C67. The proposed method was developed because until 2017 there was no Brazilian Standard to evaluate the efflorescence potential for brick and structural clay tile. The method uses 2 × 2 × 20-cm specimens immersed in 5-cm of distilled water for 5 days in recipients covered with a rubber membrane. The method uses smaller samples than the standard method and has a 5-day instead of 7-day duration. Ceramic blocks from ten manufacturers from different Brazilian regions were used in this study. Results from the standard test method indicated that blocks from three manufacturers were susceptible to efflorescence while the results from the proposed method indicated that the blocks were not susceptible to efflorescence. The discrepancy in results may have been caused by the very small size of the specimens and the large amount of water in the containers used in the proposed method. The amount of soluble salts in the small specimens may not have been enough to detect their presence and the soluble salts in the submerged part of a specimen may have simply dissolved by the water.

Compressive strength of masonry constructed with high strength concrete blocks

Resumo Although the use of high strength concrete blocks for the construction of tall buildings is becoming common in Brazil, their mechanical properties and behavior are not fully understood. The literature shows a gap in experimental studies with the use of high strength concrete blocks, i.e., those with compressive strength greater than 16 MPa. The work presented herein was conducted in order to study the behavior of high strength structural masonry. Therefore, the compressive strength and modulus of elasticity of concrete block walls tested under axial load were assessed. The specimens included grouted and ungrouted walls and walls with a mid-height bond beam; ungrouted walls were constructed with faceshell and full mortar bedding. The walls were built and tested in the laboratory of CESP and in the Structures Laboratory of the UNESP Civil Engineering Department in Ilha Solteira (NEPAE). Concrete blocks with nominal compressive strength of 16 (B1), 24 (B2) and 30 (B3) MPa were used. Ungrouted masonry walls had a height of 220 cm and a width of 120 cm while grouted masonry walls had a height of 220 cm and a width of 80 cm. Traditional Portland cement, sand and lime mortar was used. The testing program included 36 blocks, 18 prisms, 9 ungrouted walls (6 with face-shell mortar bedding and 3 with full mortar bedding), 9 grouted masonry walls, and 12 ungrouted walls with a bond beam at mid-height. The experimental results were used to determine the compressive strength ratio between masonry units, prisms and masonry walls. The analyses included assessing the cracking pattern, the mode of failure and the stress-strain curve of the masonry walls. Tests results indicate that the prism-to-unit strength ratio varies according to the block strength; that face-shell mortar bedding is suitable for high strength concrete masonry; and that 20% resistance decrease for face-shell mortar bedding when compared with full mortar bedding is a conservative consideration. The results also show that using a bond beam at the mid-height of the wall does not lead to a compressive strength decreased but it changes the failure mode and the shape of the stress-strain curve. In addition, the results show that estimating E = 800 fp is conservative for ungrouted masonry walls but reasonably accurate for grouted masonry walls and that there is no reason to limit the value of E to a maximum value of 16 GPa. Furthermore, the results show that, for design purposes, a wall-to-prism strength ratio value of 0.7 may be used for high strength concrete masonry.

Compressive and Time-Dependent Strength of Concrete Masonry Constructed with Type M Mortar and Grouts Containing High Volume of Fly Ash and Slag

A testing program was conducted to determine whether concrete masonry prisms constructed with Type M mortar and grouts containing high volumes of supplemental cementitious materials (SCMs) could meet minimum masonry compressive strength requirements. Research focused on replacing portland cement (PC) with Class F fly ash and ground-granulated blast-furnace slag (GGBFS) in quantities larger than those currently allowed by technical standards. In addition, the research evaluated the development of the compressive strength of the prisms with time. Thus, specimens were tested at 14, 28, 42, 56, and 90 days. The control prism group contained grout with only PC. In the second prism group, the grout had Class F fly ash replacing PC at rates of 45, 55, and 65% while in the third prism group the grout had Class F fly ash and GGBFS combinations replacing PC at rates of 65, 75, and 85%. The compressive strength of all prisms exceeded the minimum compressive strength requirement of 10.34 MPa (1500 psi) at 28 days, although the 65% fly ash grout mixture itself did not meet the minimum grout compressive strength of 13.79 MPa (2000 psi) at 28 days. A lower estimate of the ultimate strength of grouted prisms constructed with grouts containing high volumes of SCM can be estimated by multiplying the strength measured at 14 days by 1.2 and 1.3 for prisms with binary and ternary grouts, respectively.

Strength of Hollow Concrete Masonry Reinforced with Sprayed Glass-Fiber-Reinforced Polymer

The results of out-of-plane strength tests on unreinforced and reinforced concrete masonry wallettes that were constructed using 190×190×390-mm hollow concrete masonry units are reported in this paper. The reinforcement was external and was accomplished by spraying one side of the wallettes with layers of glass-fiber-reinforced polymer (GFRP). Eight unreinforced and 28 reinforced wallettes were constructed and tested in four-point bending spanning either vertically or horizontally. Twelve additional reinforced wallettes were constructed but tested cantilevered from either the bottom or one of the sides and loaded either along the top or along the nonsupported side. Overall, the results indicate that the strength of unreinforced masonry can be greatly improved by external reinforcement. The behavior of the wallettes is also discussed, with the most worrisome observed behavior being the failure of the webs of the masonry units in the direction parallel to the direction of the applied loads. As part of the research, simplified models to predict the capacity of hollow concrete masonry externally reinforced with sprayed GFRP were also developed and presented in this paper.