## Spinning Spherical Target: Probability for Three Marksmen to Hit on the Same Hemisphere

**Problem**

Three marksman simultaneously shoot and hit a rapidly spinning spherical target. What is the probability that the three points of impact lie on the same hemisphere?

A. 0 | C. 1 |

B. 1/2 | D. 2/3 |

## Example 02: Notched beam with concentrated load

**Problem**

A 150 mm by 300 mm wooden beam having a simple span of 6 meters carries a concentrated load *P* at its midspan. It is notched at the supports as shown in the figure. For this problem, all calculations are based on shear alone using the 2010 NSCP specification given below. Allowable shear stress of wood, *F _{v}* = 1.0 MPa.

- If
*P*= 30 kN, calculate the maximum allowable depth (millimeters) of notches at the supports.- 88
- 62
- 238
- 212

- If the depth of notches is 100 mm, what is the safe value of
*P*(kiloNewton) the beam can carry.- 26.67
- 17.78
- 8.89
- 13.33

- If
*P*= 25 kN and the depth of notches is 150 millimeters, what is the shear stress (MegaPascal) near the supports.- 0.83
- 6.67
- 1.67
- 3.33

**NSCP 2010 Section 616.4: Horizontal Shear in Notched Beams**

When rectangular-shaped girder, beams or joists are notched at points of support on the tension side, they shall meet the design requirements of that section in bending and in shear. The horizontal shear stress at such point shall be calculated by:

Where:

$d'$ = actual depth of beam at notch.

## Example 01: Safe Uniform Load for a Beam that was Notched at the Tension Fibers at Supports

**Problem**

A 75 mm × 150 mm beam carries a uniform load *w _{o}* over the entire span of 1.2 m. Square notches 25 mm deep are provided at the bottom of the beam at the supports. Calculate the safe value of

*w*based on shear alone.

_{o}Allowable shear normal to grain = 1.85 MPa

## Example 02: Maximum Concentrated Load a Box Beam Can Carry

**Problem**

A beam is built up by nailing together 25 mm thick planks to form a 200 mm × 250 mm box section as shown. The nails are spaced 125 mm apart and each can carry a shearing force of up to 1.3 kN. The beam is simply supported for a span of 3.6 m and to carry a concentrated load *P* at the third point of the span. The allowable shearing stress of the section is 0.827 MPa.

- Determine the largest value of
*P*that will not exceed the allowable shearing stress of the beam or the allowable shearing force of the nails. - What is the maximum flexural stress of the beam for the load
*P*computed in Part (1)?

## Example 01: Spacing of Screws in Box Beam made from Rectangular Wood

**Problem**

A concentrated load *P* is carried at midspan by a simply supported 4-m span beam. The beam is made of 40-mm by 150-mm timber screwed together, as shown. The maximum flexural stress developed is 8.3 MPa and each screw can resist 890 N of shear force.

- Determine the spacing of screws at
*A*. - Determine the spacing of screws at
*B*.

## Example 04: Required Depth of Rectangular Timber Beam Based on Allowable Bending, Shear, and Deflection

**Problem**

A beam 100 mm wide is to be loaded with 3 kN concentrated loads spaced uniformly at 0.40 m on centers throughout the 5 m span. The following data are given:

Allowable shear stress = 1.24 MPa

Allowable deflection = 1/240 of span

Modulus of elasticity = 18,600 MPa

Weight of wood = 8 kN/m

^{3}

- Find the depth
*d*considering bending stress only. - Determine the depth
*d*considering shear stress only. - Calculate the depth
*d*considering deflection only.

## Working Stresses of Philippine Woods at 50% Stress Grade

**Working Stresses for Visually Stress-Graded Unseasoned Structural Timber of Philippine Woods**

Species |
50% Stress Grade |
||||

Bending & Tension Parallel to Grain | Modulus of Elasticity in Bending | Compression Parallel to grain | Cpmpression Perpendicular to Grain | Shear parallel to Grain | |

MPa | GPa | MPa | MPa | MPa |

## Working Stresses of Philippine Woods at 80% Stress Grade

**Working Stresses for Visually Stress-Graded Unseasoned Structural Timber of Philippine Woods**

Species |
80% Stress Grade |
||||

Bending & Tension Parallel to Grain | Modulus of Elasticity in Bending | Compression Parallel to grain | Compression Perpendicular to Grain | Shear parallel to Grain | |

MPa | GPa | MPa | MPa | MPa |

## Allowable Loads on One Bolt in Timber Connection

## Group Species of Philippine Wood

I. High Strength Group |
II. Moderately High Strength Group |
III. Medium Strength Group |
IV. Moderately Low Strength Group |

Agoho Liusin Malabayabas Manggachapui Molave Narig Sasalit Yakal |
Antipolo Binggas Bokbok Dao Gatasan Guijo Kamagong Kamatog Katmon Kato Lomarau Mahogany, Big-leafed Makaasim Malakauayan Narra Pahutan |
Apitong Bagtikan Dangkalan Gisau Lanutan-bagyo Lauan Malaanonang Malasaging Malugai Miau Nato Palosapis Pine Salakin Vidal lanutan |
Almaciga Bayok Lingo-lingo Mangasinoro Raintree Yemane |